So, I was wandering around Riften, when Erikur appeared in front of me and told me that I attacked his family(true), and I needed to apologize and leave them alone or else he would kill me.

And I was like.. "COME AT ME BRO"

And he was like... "I'LL BRO"

Then I sliced him with my lightsaber and ripped his heart off with my bare hands. (You know, mods.)

And that blonde-guy-follower you get from Dawnguard was like "Wth yo cant do that bro!"die!11eleven"

So I ripped his heart off too.

Then me and Serana..well..we killed everyone on Riften, there was like...30 guards trying to kill us.

What have I done? Will I need to talk to Erikur/that blonde guy somewhere in the future?

okay, aside from me not knowing if any of that dialogue even exists in game...

Erikur lives in Solitude... not Riften...

be careful man, putting mods into your game can have hazardous results..

Also, Erikur is set as essential in the vanilla game. If he was planning to complete the Thieves' Guild quests, he just screwed himself out of that.

Erikur is no longer essential once "Bound Until Death" is completed.

This is a rare world interaction that may occur if you cause bodily harm to a member of an NPC's family. Honestly, given the carnage you caused, wouldn't the slight wounding of your pride from simply apologizing to Erikur be preferable to the death of the majority of a town -- including merchants and questgivers?

He ripped his friend's heart out; obviously he has no [censored]s to give in these streets.

At least you could follow what ever it was he was talking about lol