Satan's Folly has an Errata:
Satan’s Folly
Type: Hero Enh. • Brigade: White • Ability: None • Class: None • Special Ability: If one of holder's Heroes is about to be discarded, Holder may substitute an Evil Character from an opponent's territory in place of the Hero being discarded. • Errata: If a Hero is discarded later in this battle, discard an Evil Character in an opponent’s territory to heal that Hero. • Identifiers: None • Verse: Colossians 2:15 • Availability: Apostles
The errata specifies "a" hero, so only one hero can be healed.
