There is.When hero dies you cant revive him unless you created a trigger for... but you surely didnt so no problems, just do as inevit4ble said,i confirm.But there's probably a field in the object editor either on the hero itself or on the altar to set whether the hero can be revived or if the altar can revive that hero
Techtree - Revive Dead Heroes = False is what you wantOr go to the alter and disable the "Can Revive Heroes" thing.