To recast or not recast: That was the big question facing many showrunners for the 2018-19 television season, after the exits — both planned and unplanned —of some integral series stars.

After Clayne Crawford was fired from “Lethal Weapon” for abusive on-set behavior, the Fox drama’s fate was in limbo. Studio Warner Bros. worked to replace their co-lead in order to stand a better chance at the third season getting on the schedule. They struck a deal with Seann William Scott, giving the film star his first regular role on the small screen, and it proved to be the key.

“If we could not feel confident to bring that show back with a great cast in a way that the audience would accept it, we would have simply not brought the show back,” Fox TV Group boss Gary Newman admitted during the network’s Television Critics Assn. panel in August. “Until they came up with Seann, we were planning a schedule without ‘Lethal Weapon.'”

Newman said there was never any consideration for recasting Crawford’s role of Martin Riggs, so instead the broadcaster chose to renew “Lethal Weapon” with Scott stepping in as Damon Wayans’ new on-screen partner, veteran Wesley Cole, a character Newman said was “very much informed” by Scott himself.

Fellow Fox drama “9-1-1” is also setting out to introduce two new characters in the wake of season 1 star Connie Britton’s departure. Britton had only a one-season contract and opted not to renew, instead moving on to Bravo’s “Dirty John” anthology drama, in addition to her role on Showtime’s “SMILF.”

While producers and network executives say the “door is open” for Britton should she want to return to “9-1-1” down the line, the second season will shake up characters and relationships through the cast additions of Jennifer Love Hewitt and Ryan Guzman.

Hewitt’s character, Maddie Kendall, is Buck’s (Oliver Stark) older sister who “freshly” arrives in Los Angeles in the second season premiere, “looking to start over, having just escaped an abusive relationship,” says co-creator and showrunner Tim Minear.

“Not only is the first time she’s seen Buck in a while, but the new man he’s become since meeting [Britton’s] Abby is in many ways wholly unrecognizable from the immature womanizing younger brother she remembers,” Minear continues. “Buck is still very much holding a torch for Abby, so Maddie will fill sort of an emotional void that’s been created there, in addition to also filling the open station of a 911-operator.”

With Guzman as Eddie Diaz, a former Army combat medic who has made the transition to firefighter, Minear says he will represent “some real competition for Buck.” But he also allows the show a way into telling more poignant family stories, as he is “a single father caring for a special needs son,” adds Minear.

ABC faced a similar dilemma after “Roseanne” star Roseanne Barr sent a racist tweet and the network decided to cut ties with her. Initially the Alphabet canceled the sitcom revival, but a month later struck a deal to create a new series, “The Conners,” centered on the rest of the family, with Barr written out of the show.

Barr’s absence “irrevocably changes” the family dynamics, says showrunner Bruce Helford, and opens it up to be more of a true ensemble.

“There is a ‘we’re on our own’ quality that encourages each of the family members to take more risks in their life choices, jobs, and romantic involvements — and this includes all generations of the Conners,” he says.

Without Barr (whose character will reportedly be killed off), John Goodman’s character of Dan will have to take a “more hands-on approach” to the family, especially the grandchildren, says Helford, while Darlene (Sara Gilbert), Becky (Lecy Goranson) and Jackie (Laurie Metcalf) take on more responsibilities as well, stepping in as the family’s “heads of household.” Helford also decided to bring on a new maternal figure in the still-to-be-cast role of DJ’s wife, Geena.

And “NCIS” showrunners had to figure out how to fill the shoes of Abby Sciuto after Pauley Perrette opted to leave the CBS drama in its 15th season. The forensic scientist was a fan favorite, and Frank Cardea and Steven D. Binder admit that replacing such an iconic character was a “daunting task.”

Although Kasie Hines, played by Diona Reasonover, who has been upped to series regular in season 16, is also a forensic scientist, she’s not intended to fill Abby’s formidable shoes.

“In contrast to our other characters, who are all highly experienced and somewhat hardened federal agents, Kasie [has] the eyes of a newcomer,” the showrunners say, “and with that, an unjaded enthusiasm that will prove to be infectious to her co-workers.”

And then there are those producers who are willing to get creative with casting, finding a new actor to play the same role.

On the CW, the final season of Rachel Bloom and Aline Brosh McKenna’s “Crazy Ex-Girlfriend” will include a return of first-season love interest Greg. The role was originally played by Santino Fontana, who had a one-season contract for the series and opted only to return as a guest star in the second year. At the time, he was written out so the actor could pursue other projects — and the character was sent off to Emory University.

In wrapping up the series’ run, the co-creators wanted to bring back someone who was pivotal to Rebecca’s (Bloom) early journey. With Fontana still unavailable, they are bringing the character back in a “re-imagined way,” with Skylar Astin stepping into the role. That also allows them to play with the idea of “perception,” as Rebecca has only recently started to get healthy after struggling for years with her mental health.

“Greg resolved many of his personal issues before he left, but almost none of his issues with Rebecca, so we’re excited to explore their dynamic now that they’re both in different types of recovery,” Brosh McKenna says.

Similarly, when Fox resurrected Tim Allen’s family comedy “Last Man Standing” a year after it had been canceled by ABC, not all of its original cast members were still available. Given that the show focuses on the Baxter family, producers felt it imperative to be able to include all of the original characters. Molly McCook was brought in to replace Molly Ephraim as Mandy, while Jet Jurgensmeyer was hired to play Boyd.

“Mandy grew seven inches and became a blonde,” showrunner Kevin Abbott jokes.

The show is also bringing in an additional new teenage character, yet to be cast — Jen, a foreign exchange student from Hong Kong who is coming to stay with Mike and Vanessa. “Jen will offer an outsider’s perspective on the cultural norms of American life, as well as challenge Mike’s view of America’s place and responsibilities in the world,” says Abbott.

Other shows, including NBC’s family drama “This Is Us,” CW’s female superhero drama “Supergirl,” and Fox’s medical drama “The Resident,” are also reinvigorating main characters’ storylines through the introduction or expansion of new players.

Chris Wood departed “Supergirl” after the third season, but the show opted not to merely replace him with another love interest for Kara (Melissa Benoist). Instead they focused on building out the strong female cast, and confirm their commitment to inclusion with introducing TV’s first transgender superhero.

Nicole Maines will play Nia Nal, whose arc will parallel Kara’s first season journey. But she will also challenge and inspire Kara to take on a mentorship role. Nia not only works as an “eager, ebullient new reporter at Catco,” according to executive producers Jessica Queller and Robert Rovner, but she is also experiencing new powers, specifically the ability to see the future in her dreams, and has to “learn how to use them and claim her role as hero.”

“The Resident” is complicating the personal and professional lives of its characters through Glenn Morshower as Marshall Winthrop, Conrad’s (Matt Czuchry) estranged father.

“A resident can’t overrule a CEO or a chief of surgery. But the Chairman of the Board can,” says showrunner Todd Harthan. “That means it’s ‘Game of Thrones’ in the power centers of the hospital and [Dr. Randolph] Bell has a serious adversary in Marshall.”

And Jenna Dewan’s recurring role of Julian Lynn, a medical device rep who blows into the hospital, is going to push the show into “thriller” territory, adds Harthan. She will not only threaten Devon’s (Manish Dayal) future marriage but also his career as a doctor.

Meanwhile, “This Is Us” has bumped Lyric Ross up to a series regular for its third season, promising Randall (Sterling K. Brown) and Beth (Susan Kelechi Watson) will be involved in their foster care/adoption journey for the long haul, and Beth’s cousin Zoe (Melanie Liburd) is also “joining the show in a big way,” according to co-showrunners Isaac Aptaker and Elizabeth Berger.

“She begins dating Kevin,” they confirm. “It’s a really fun romantic comedy dynamic…and then the fact that she’s related to Beth just makes the whole thing a lot messier and more complicated and fraught.”