I was in Whitrun, stacking stuff in my house and running errands between wanderings, when Idolaf Battle-Born said somthing rude (as he always does). I lost it for a moment and unarmed my weapon and svcker punched him in the head from behind. Felt good for a moment, a brief moment. Then I discovered Golldir who is my following NPC right now (I have not killed this one yet) went on full attack with a very nice greatsword. It was over in seconds and I could not stop him. I was fined 40 gold by the guards and nothing else was said. Is this going to be a issue down the road?

It should be fine, he is part of a side quest but there are two other people who can give you that same quest.

Bounty of 40 gold? That would mean he wasn't killed. So you should be fine.

I thought he is essential? If you got a bounty of only 40 gold, you probably haven't killed him.

This IS Skyrim, consequences don't exist. You'll be fine.