Well in the "Ultimates" universe, Peter is already dead and has been replaced by a different kid who took up the Spider-Man name, so this doesn't come as a surprise. Thing is, in the Ultimates version, that death seems to be sticking (ha! pun) but in the classic universe, death never lasts, so if Peter does die or if Doc Ock does, you'll be sure to see him make a return eventually.