If you release it and don't kill it, you can not release it again, so you will have to buy The Ring of the Count
from a player or from Black Bert
to continue The Inquisition Quest
. If you put 3 garlic necklaces
on the stones around the buried coffin, you can save yourself a lot of troubles, after that The Weakened Count
appears (looks the same as regular vampire and causes the same damage).