According to the Hollywood Reporter, the original rights-holders to the movie "Buffy the Vampire Slayer" are planning a "remake/relaunch" featuring the character:
"While Whedon is the person most associated with "Buffy," Kuzui and her Kuzui Enterprises have held onto the rights since the beginning, when she discovered the "Buffy" script from then-unknown Whedon. She developed the script while her husband put together the financing to make the 1992 movie, which was released by Fox."
Which made me think back to the 80s Filmation "Ghostbusters" cartoon -- you know, that cartoon that you watched as a kid and made you say: "hey, that's not the Ghostbusters." The cartoon was based on an old TV show called "The Ghost Busters," and was similar to the just-released popular "Ghostbusters" movie only in name. But Filmation owned that name -- forcing Columbia Pictures to obtain the rights to it for the hit film. That's why the official animated adaptation of the Ivan Reitman movie was named "The Real Ghostbusters."
So in theory, Kuzui Enterprises could pull a "Ghostbusters" and have their own version of Buffy Summers. They could use all the characters from their original film: Buffy, Merrick, Pike. But would 20th Century Fox & Joss Whedon let them without a lawsuit? Alternatively, could Kuzui turn around and force the existing BTVS franchise rename themselves "The Real Buffy?"