In a shakeup at Warner Bros.-based Silver Pictures, Navid McIlhargey will leave to become a senior VP at New Regency, and Silver Pictures prexy Susan Downey has told Joel Silver that she will not renew her contract when it expires next February.

That has fueled speculation that she will leave to form a production company with her husband, Robert Downey Jr.

McIlhargey was let out of his contract by Silver and is expected to leave quickly for New Regency, Arnon Milchan’s production-financing company which is ramping up under Robert Harper and Hutch Parker.

The toppers called McIlhargey their final key creative exec hire, joining recently hired ex-Paramount Vantage exec Amy Israel and Regency vet Kara Francis.

Among the high-profile films McIlhargey shepherded at Silver Pictures was “RocknRolla,” the Guy Ritchie-directed drama that will be released Oct. 31 through Silver’s Dark Castle label.

Less certain is the next move for Downey, a 10-year vet who will continue to oversee creative projects generated both at Silver Pictures and Dark Castle until her deal expires in February. She’s focusing on producing “Sherlock Holmes” with Silver, Dan Lin and Lionel Wigram. The Ritchie-directed period pic stars her husband as the title sleuth.

Although Silver Pictures sources said Downey is still figuring out how she’ll redefine her role at the production company, it would hardly be a surprise if she left to form a company with her husband.Silver will replace McIlhargey, but it is not immediately clear whether he’ll promote from within. Dark Castle has veeps Erik Olsen and David Gambino, and Downey shares the president title at Dark Castle with Steve Richards, the Silver Pictures chief operating officer who’s primarily a business executive.

Silver has had a rough run of late with B.O. disappointments “Fred Claus” and “Speed Racer.” The tenured WB-based producer’s deal is up in late 2009, but there is no indication that his 22-year run at the studio is in jeopardy.

Dark Castle, which finances its genre films and distributes through WB, is aligned to WB through late 2011. Aside from “Sherlock Holmes,” Silver Pictures is producing “Book of Eli,” the Allen and Albert Hughes-directed drama that will star Denzel Washington. Silver is also prepping a remake of “Logan’s Run,” among other projects.

On the Dark Castle side, Silver’s in post-production on the Kate Beckinsale starrer “Whiteout,” the Peter Sarsgaard-Vera Farmiga starrer “Orphan,” John Cusack starrer “The Factory” and the James McTeigue-directed “Ninja Assassin.”