Hi,
I asked a question about "Reclaim the fallen", as a Hero called from the discard pile can be put in play in a zone with a Hero already on it, and about playing this tactic while having two heroes on my discard pile.
Here is the answer :
In the situation you describe, one of the heroes will fizzle. Reclaim the fallen, once the cost is payed, is an effect that you fulfill as much as possible. So the player who played Reclaim The Fallen will get to decide which Hero to keep when both start in the discard pile. When one is already in play, the one in the discard pile will not enter play since that would cause an illegal state.
Hope that helps,
Lukas