So I accidently left the covenant before killing Shiva's ninja body guard and getting this sweet ring. Before I waste souls on absolving my sins and rejoining the covenant I want to make sure that Shiva and his ninja respawn after having broken the covenant.

They'll be there.
 
Edit: Make sure you're actually prevented from rejoining before you pay up, I've found needing absolution to be kind of inconsistent.

I believe if you left the convenant by joining another there's no need to absolve, and you can easily rejoin.

You only get one chance to kill the ninja. Its easiest in blightown - especially if you lure a spider over to attack you, hide behind the ninja and he will hit the ninja at the same time. Shiva will only attack you once the ninja dies. Probably a lame method, but it works.

Excellent. I'll give it a shot when I'm a higher level, going to make sure I'm powerful enough that I don't mess it up.

no, it's easiest in the forest. kick him a few times, he won't even aggro. just make sure to quit as soon as the souls register in your account. reload and it'll be where he was sitting.

I thought they moved him in the latest patch so you can't kick him off the ledge?