If anyone survives the series, I think it'll be Lupin. The only reason I think so is because it seems almost too much to kill off the whole Marauders generation, as it were. James and Sirius are already dead, and Peter is sure to die in Book Seven saving Harry in some fashion (as, I fear, is Severus), so that leaves Lupin by default, as it were.

On the other hand, JKR keeps going on and on about how grey and old Lupin is looking, so she might be telling us not to get too attached to him...

Thanks v. much for your comments.