Board Thread:Theories and Speculation/@comment-27924662-20160917205629/@comment-734582-20160918074536

The choice wasn't much of a choice, he was dead the moment Sasuke and Obito appeared. Obito would never allow him to land the killing blow on Sasuke.

Kotoamatsukami on either Obito or Sasuke would likely not have worked, we saw how easily it's broken if a bystander is aware of it. Anomalous behaviour in Sasuke or Obito would've ensured the other broke it. Both were hellbent on destruction so it's not like there was a subtle command that could fly under the radar and save the world.

Izanagi wouldn't have bought him any time because of what i said first: He wouldn't be allowed to strike a killing blow.