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I've always been a fan of allowing priest/heroes to die if they get too bad of a beating when preaching or performing other priest actions. Maybe compensate by giving them a slightly higher conversion rate when preaching.
I meant gameplay wise as a hero you need to have been in a battle recently to tell tales right?
No
But the Priest Hero combination as far as I know has no difference from a regular priest, so it's not a very attractive combination to take.It actually takes away one of the defining characteristics of a hero (the ability to die in battle) since priests can't participate in battles.