So a Spriggan turns your dog against you. You kill the Spriggan, and are left with a dog that has been turned. Can you stop his attacks with Calm, or Command Animal?

hmmm....not sure. there's also a shout you get you can try....

I'm mostly wondering if you can over-ride the spriggan's spell once it's dead.

since i've not seen this asked before and i haven't tested it myself yet (spriggans seem to be few and far between for me not to mention i don't care for any type of follower/companion), maybe someone else can answer. i imagine it's possible. just make a save and test it out.

if it's a spell they cast, it should wear off after the spell expires......

That's my thinking. I guess I'll have to try it out in Eldergloom or Balor's cave......