enemy hero (quests)
 

as most of them does not have a quest related to them, i just wait till the end of each map to clear the enemy heroes.

i noticed if they have an associated quest, and if i kill them before i initiate that quest, it would no longer be available.

such as the polar bear plea quest to get rid of the poacher, on umkas.
now i wonder how many quest i missed this way. is there a list? or better question, are all enemy hero related quest limited to each map only? (meaning, the quest will not send you to another island to kill an hero, you can really miss the quest by clearing an island then find out another island was going to give you the quest to get rid of that enemy hero)

read this:
http://forum.1cpublishing.eu/showthread.php?t=11137
and look for a mod in the mod topics. there is one that puts an asterisk next to heroes' names for those heroes involved in a quest.

Oh wow; I was actually wondering the same thing as the op; this is a nifty mod maybe they will make it a part of the game.