Small clarification: Raise Dead cannot return an undead creature to life, as in - it cannot bring back a slain vampire as a vampire.... Nor can it bring back a currently animated undead creature to life (i.e transform a ghoul back into a human for example).
Once an undead creature is destroyed however, it is just a corpse. As such - it can be returned to life by any of the normal means.
Well, once a zombie is killed it's the corpse of a zombie, not the corpse of a human. And then there's the whole issue of PCs turned into incorporeal undead, with no corpse to resurrect.
But who cares? Permanent death is bad news bears. I like the AL solution to being vamped a lot, even if it doesn't completely jive with the Buffy the Vampire Slayer mystique of vampires exploding into dust when slain.