You're probably going to have to do it for triggers. Not exactly aware how you'd do that right now, but maybe you can make it so that when the spell is cast, heroes in the area will rise up. As the above poster said, you need to be a little more specific.
Ok, ive got the triggers all ready, and I have a way that when the spell is cast, heros that have fallen in the area will be revived, but the problem is whenever the spell is used it uses mana, even if their arent any heros dead, the spell can always be used, this is a major glitch and it would be corny if i couldnt fix it