So I sacrificed Torvald, the annoying drunk from the companions, to Boheith back when I was level 40 now at level 70 he has suddenly reappeared again in Jorvaskr. Luckily he doesn't seem to hold a grudge. I wonder why he showed up again?

My Shadowmere horse respawned. So I guess it is supposed to happen.

Shadowmere is an undead horse, so it usually re-spawns. I don't know why the other guy did though.

Skjor also returned after a few days of his death, so you are not alone. I guess it is some bug then.
but on the bright side, u killed a guy, he came back to life, he didnt yell at you for pulling his pants down. well done