I've heard that if you spare Sinding, you find him roaming in Skyrim fighting bandits. Of course, despite the better nature of my character thinking initially to spare him, if this is seen - my character, knowing he went against his word, will kill him... however - that begs the question - if you see him roaming outside like that, can you kill him? And if you do so, does that prevent future encounters with him like this?

Many thanks!

i have never seen him roaming outside after that quest he says he can be found in grotto but actually doesnt stay there he is disabled i think after that quest i may be wrong but i have never seen him after that quest.

Several copies of him spawn due to bugs and he may be found wandering around Riverwood and Helgen, but he's not supposed to show up anywhere other than the Grotto.

I thought a Dawngaurd added Werewolf was Sinding, until My character was at half Health. I just knew that Werewolf near Helgen was Sinding

Does that happen if you kill Sinding during the quest, or only if you spare him?

Both, I think. And, he's on his best behavior when wandering Riverwood!