We know what to expect of him. We know they are unstable, we have more skilled allies, we have more allies- and we have time to brace for our next meeting. There is no reason we will not be able to handle them ourselves in the future.

Failing that- there is always Cortana. She seems to have imprinted upon them somewhat in a protective curiosity. It never hurts to have a digital Valkyrie to call upon their enemies.