Your hero player is complaining about a 45 to 13 lead?!? How on earth is that too hard for the heroes?!? Someone needs to smack that guy! Usually in RtL, especially if the heroes aren't used to how to Blitz, it's the other way around (OL has 40+, heroes lucky if they have 15).
As for Threat at the end of a dungeon/encounter, it's simply lost, returned to the threat pile.
-shnar