I swear I remember reading something about heroes not getting rewards for killing leaders/Lts with lingering effects. The only related item I'm coming up with is that curse tokens are not gained by killing Master Dark Priests with lingering effects.
A strict reading of the RtL rules states that when a hero "deals a killing blow" to an encounter leader the party is rewarded (pg 14, last sentence). But the Lt is more vague - it merely states "When a hero kills a Lt". I thought there was an official ruling on this, but I'm not coming up with anything.
Do heroes still gain rewards for bleeding/burning/what-have-you a leader or Lt to death? The OL rules are pretty clear cut- "when a hero dies" he gains conquest, but sadly, the hero rules are not...