To paraphrase an old song, “You picked a fine time to leave me, ‘Law & Order.'”

NBC came to rely so heavily on “Law & Order”-branded shows during the Zucker years that the inevitable fading of the franchise was a bill that had to come due sooner or later.

It looks like that time is now, right after Comcast took over, as the new team tries to steady the network’s primetime lineup. Good timing again, Jeff.

First, NBC passed on renewing the mother ship, much to the chagrin of producer Dick Wolf. Then the network ordered “Law & Order: Los Angeles,” cynically rejiggered the show in midstream, and watched the ratings founder. Finally, the most durable entry, “Special Victims Unit,” is losing leads Christopher Meloni and, eventually, Mariska Hargitay.

It’s not like they’re rats deserting the ship after — what, a hundred seasons? — and “L&O” has certainly demonstrated the ability to survive changes in the past. But it’s almost undeniable that the franchise’s glory days are long behind it, a product of natural erosion and the greed that launched “Law”-branded spinoffs like “Criminal Intent” (still on USA), “Trial by Jury” and the reality show “Arrest & Trial.”

Series architect Wolf has had a fabulous run, but all good things come to an end sooner or later. Just ask CBS, which has succumbed to similar forces in its decision to move all of the “CSI’s” to other nights and less vital timeslots.

Back in 2007, when Wolf and NBC struck an extension deal on multiple installments of the program, Wolf said it was his “ultimate dream” for “Law & Order” to surpass “Gunsmoke’s” 20-year run for a primetime drama.

Even settling for a tie, as he ultimately did, “L&O’s” place in the TV history books is secure. But despite the remnants of it that remain on the air, that’s what the franchise is now: History.