I have just completed the quest that Sinding is in, the ring of Hircine one. I chose to kill Sinding and now own the Savior's hide, I backtracked to loot everything then decided to sleep in one of the bedrolls and the entrance. I woke up to be greeted by Sinding's big hairy butt in my face as he was stood in front of me alive and well.

Why?

It's a glitch. I've run into him a few times, roaming around Skyrim in werewolf form. Killed him every time, too, but he just won't stay dead.