Sarah Michelle Gellar may be putting down her TV stake this month, but Buffy Summers and her demon-dusting legacy will live on -- in academia, of all places. ''Buffy the Vampire Slayer and Philosophy: Fear and Trembling in Sunnydale'' (Open Court, $17.95) is the latest highbrow reading of what tenure strivers call the Buffyverse. ''There's no way for a philosopher not to be provoked by themes that 'Buffy' presents,'' insists editor James B. South of Wisconsin's Marquette University. Those subjects include Willow as an Aristotelian Tragic Hero (she's not), Angel as a Kantian Rational Being (he is), and Buffy and her gang as Marxist heroes, ''the 'primitive rebels' of leftist lore and scholarship.'' (O-kay.) Amused? So is ''Buffy'' exec producer Marti Noxon: ''We do have lofty goals, but there's also the part where we're kind of scratching our butts, going 'Well, that'd be cool!'''