Friend locked out because of redzone, what can we do?

I play with a group of 3 others every wednesday and saturday. Last week, one of our friends was unable to play just as we went to >!the house of hope!<, a red zone, so we had to swap out with another camp party member.

After we  rescued hope  we called it for the night, figuring our friend could join us for >!the Raph fight!<, but we can't send back the camp member or go back to camp. Our friend also can't join the game at all as it's now locked at 3 players.

Do we really have to go back on our save or is there another way to swap out npcs in red zones?