Let me tell you a little story, in 1999 a movie came out on May 19th, it was called "Star Wars: The Phantom Menace" (well it really doesn't matter what it was called, but still) and on the same day the largely popular archive "Master & Apprentice" archive came to life and thus started a fandom with an OTP that could rival K/S, but wait, one of the characters in the main pairing was dead before the movie was done! What? And thus this fandom was strong and is still a little bit alive, 11 years after it started, while one part of it's main pairing was dead after 120 mins of screen time.
Am not afraid of Severus dying in the last HP movie, on the other hand, based on the interaction and how the director puts it to the audience I expect that the Snarry pairing might have a few new fans out there or old fans trying to fix it. Am a great believer in the power of fixit!fics, I love them in most fandoms where one of the characters might die (I mean the Star Trek people killed Kirk for crying out loud! And when I came into that fandom sometime in the 90's K/S was still going strong :)).
I expect that Snarry might die down a while after another couple of years, but I don't think it's going to disappear anytime soon.
Am worried about not having the Snarry Games anymore though *pouts* Maybe someone should think about that? *wink*