My vampire has been deleted!
There are two ways a vampire can be deleted. If a player who hasn't donated has been inactive for three consecutive weeks, their vampire is completely eradicated from the database. There is no way to get such a vampire recovered, there are no records stored of vampires deleted in this manner.
The other way a vampire can be deleted is for cheating; in these cases, the vampire is not actually stricken from the database, but rather the account is locked. This happens when a player creates several vampires and uses them as a group, pooling resources or ganging up on other vampires, or for signing up lots of vampires for the blood bonus. If this has been done in error, it is possible for a vampire to be reinstated, but it's not likely - it's usually pretty obvious when it's cheating and when it's not.