Not possible, you say? You're probably right, but humor me.
Scenario: I make a rescue attempt with Lazarus (Di). My opponent blocks with a character that doesn't negate Lazarus' ability. I play Ambush the City. I start a new rescue attempt and win it, rescuing a soul. The previous battle, which was a rescue attempt and became a battle challenge when I played AtC, continues. I let Lazarus die. Can I start another battle? When Lazarus' ability activated, the battle was a rescue attempt, so I assume a "trigger" was set that gets activated when the rescue attempt fails and Lazarus dies.
Also, would it make a difference if Darius' Decree was active and I used its ability while AtC battle was going on and Lazarus was set aside? This would discard him, but he was not in battle - would his "trigger" still work?
Lazarus (Di)
Type: Hero Char. • Brigade: Yellow • Ability: 4 / 5 • Class: None • Special Ability: If Lazarus is discarded and your rescue attempt fails, search discard pile for a good convert Enhancement and you may begin a new battle.
Ambush the City (Ki)
Type: Hero Enh. • Brigade: Yellow • Ability: None • Class: None • Special Ability: If making a rescue attempt, set all cards in battle aside (regardless of immunity). Holder may begin a new rescue attempt against same player. Once new rescue attempt is completed, the original battle resumes as a battle challenge. Cannot be negated.
Darius' Decree (TP)
Type: Artifact • Brigade: None • Ability: None • Class: None • Special Ability: Opponents may not play good Enhancements from hand, unless an Evil Character is in battle. You may discard this card to discard all Heroes in set-aside areas.