A series of events involving Marie LeVeau, Victor Strange and the Vampiric Verses from the Book of the Vishanti reversed the Montesi Formula in a story beginning around Doctor Strange (3rd series) #13. Only the existence of vampires was restored...individual dead vampires should have remained dead, although a few did return through other means, including Dracula. Unfortunately, after a few years it seemed Marvel basically forgot the Montesi Formula was ever cast, and centuries old vampires started showing up when they really shouldn't.
Incidentally, a spell was cast in the last Blade series which really did bring back every vampire who was ever destroyed, from both before and after the Montesi Formula.