Yep, pretty much my thoughts here. Maybe he'll stay around with the Order anyway, though. Malack seems to be able to be personally rational and unlike Belkar I feel like Durkon has enough reputation with the Order that they would look at him as a vampire and go "oh man, that sucks...let's head to the next gate."
Spoiler, you're implying that this is the last play.
Oh and a question: are we going to learn how this will affect Durkon's allegiance to Thor? Can that be removed by this change, forcing him to lose his clerical magic until he finds a new source of power?