What are the best ways to kill all those enemies in the helm? I run out of spells. I have the Gith, a brain and myself the wizard. Should we try to leave and restore and then come back?
I ran past most of them, using bonus action to Dash in order to clear more ground.
You're repeatedly encouraged during the encounter to "just run for it" and it's hinted strongly multiple times that you need to get out of there ASAP.
You don't need to kill them.