do I need to keep Demenion alive for a quest?
 

Just rounding up the path Debir-Scarlet-Bolo-Verona-Rusty-Scarlet-Debir-Verona-Montero-Verona; my question is, do I need to keep Demenion alive to complete a quest later on in the game? Is there a bounty on his head? Do I need him alive to complete the Demenion's Secret quest?

So far I have gotten 2 out of 2 Ancient Knowledge scrolls from Elenhel via the replay-battle-differently trick. As such, I decided to start using AKs killing the heroes of Montero and Verona (at least those that would end up giving me 6,000+ XP with the AK scroll on) since I may have a surplus of it if Elenhel keeps giving me AK scrolls every 30 battles. My level jumped up quite a bit, allowing me to take out all heroes at Montero and Verona (even the Driller).

So is it ok to kill Demenion this early (see attached screenshot)?

It won't be a problem, you only need to talk to Krause about the Demenion's Secret quest, and if you did that already, you are good to go.

Thanks for the reply! Proceeding to mop up the small straggler enemies at Verona, then its off to Dersu for me.