I know this is brand new and I bow to Roguelikes and your work, but is there anyway to drop the 4th character?

I only ask because my friends and I don't typically run with a 4th person and when someone is around to fill a 4th in a 4 player coop its random and far between. If not I am guessing the only option is to leave them at the entrance every time so they stay out of combat and what not.

Or would it be possible to get them killed and leave them for dead?