Dessert Nomad
Adventurer
If you really need a villain to get away, then just have them escape. The PCs may not even know the method they used, and not all magical effects are listed in the spell list. But most of the time, especially in modules, it's more fun to have them play by the book and see if the players can stop their escape. You can always have someone take over their role in a future encounter.
Just a note that a druid can hard stop that plan with moonbeam (2nd level spell) and someone who can grapple - if you hold the vampire in a moonbeam, he can't move and can't change forms to get out of the grapple. Add in some counterspell fun and even a spellcaster vampire has a hard time escaping.
If I really want them to get away I'll give them something such as misty step, ability to polymorph or turn ethereal, etc. For example, a well prepared vampire can be very difficult to kill if you're in their home turf. Hurt them enough? They turn into gaseous form and disappear into vents that are scattered around their lair.
Just a note that a druid can hard stop that plan with moonbeam (2nd level spell) and someone who can grapple - if you hold the vampire in a moonbeam, he can't move and can't change forms to get out of the grapple. Add in some counterspell fun and even a spellcaster vampire has a hard time escaping.