So I did the escape from cidna mine a while back. Didn't think much after escaping. However after my return visit I see that the whole bunch of forswarn including Mr M himself were killed and lying on the street. Its a bit odd with all the town people speaking of how scared they are that he is free now. Is he important to the story or any other part of the game?

I don't consider him to be a good guy.Even with his intentions being good.He commands his soldiers to atack people and caravans on the roads,also commands them to steal mines from villagers and from stormcloack army.Also his Forswon soldiers are always trying to kill me.

Dunno, found him and the rest of the gang in a cave after my escape and they didn't offer any quests or anything. Ended up killing them all and haven't experienced any consequenses from that either.
So i don't think it matters.

Yeah, I offed him in the middle of Markarth's forge during the escape, nobody seemed to react even to the fact that he was dead, and they still suspected me of being a forsworn collaborator. At least he isn't arbitrarily essential.

i don't want him killing people in markarth since thats where i live, so he gets killed down in the mine as soon as i see him, he's like roy phillips from FO3 to me, as soon as i saw him i killed him too..since i liked tenpenny tower people..so yeah you can kill him and it will prevent his men from killing people in markarth.

I agreed to help him escape then once he gave me that cool set of armor I killed him and got the reward for that too.

Hmm... which reward? Did I miss a quest to hunt him down?