Lapistia

I don't understand, in what way exactly? How many turns do you need to revive him within? Or will it be possible to revive several heroes randomly?

I assess the situation. If a hero falls, and his allies ignore this fact and focus on other tasks, or if it simply takes them too long to do it, the resurrection won't work, and the hero will die. Otherwise, this spell could create many absurd situations (a simple example: heroes first clear out the enemy heroes, leaving only one, and then chase him around the map/keep him stunned, while simultaneously doing something like "revive one this turn, another next turn, then drink a potion, then revive a third, etc."). I didn't focus on this aspect; I probably didn't think that such a tool would be expected of me.