Buffy's currently in its seventh series and UPN pay £1.4m to show each episode.
High-kicking super-slayer Sarah Michelle Gellar has hinted she'd like to concentrate on making films.
Mr Moonves said there might be a spin-off, or it may be replaced altogether.
But just to frustrate fans even further, he said there's always the possibility Buffy will stay to slay another day.
If networks don't want the show, it's hard for Buffy's producers to find the money to make it.