Kamui snipe GG won't last long enough for Izanami to activate...Only because of your scenario itachi wins high diff. Normal scenario he'd slaughter.
Izanami would work on obito as proven by the fact in the manga that he's trying to run away from himself.
Izanami loops him and itachi proceeds to kill him.
Rinnegan won't save him.
Izanagi won't save him.
God can't save him.
Only itachi can save him.