Enemies that change aspects of the game if left alive

Is there a list/guide something/somewhere that mentions the ramifications of letting certain characters live? came across one post by someone saying a character you let survive in the basic TOEE portion of the game shows up with cool stuff in verbobonc. I also unfortunately have always managed to kill both gremag and ravos before they got away so only just recently reading a thread here knew they had a later encounter. Would be nice to know these things, even if they are spoilerish. I looked at some full walkthroughs of the game and for the most part they seem incredibly basic and barely touch on these things sorts of "optional" events.

 

It's kind of a shame you found out about the second encounter before actually facing them. Just think how cool it would be for your party to be pretty beat up and just looking to rest and prep when BAM you're hit with some serious bad guys.

Myself, I love that kind of stuff, let's me see just how good my tactics are .... or aren't.

 

Also a shame to have played through the game many times, the majority of it anyway, but never know such an encounter occurs. Towards the bottom of he temple the game is filled with these sort of comic book character "releasing the bad guy" antics. I've never really been sure what all the later ramifications are for doing so. But with the possibility of their survival having an impact on the Co8 added stuff my interested is more piqued.

 

Yeah, I'm also curious about which characters actually will betray you down the line, and which have their own quests as NPCs. I tend not to want to bring NPCs along (not keen on giving away a share of the treasure), but if there are interesting quest/story-lines to follow from doing so, I would. Trouble is, you might just end up with someone annoying that you don't want who's busy sucking down all your gold and gear.