Let's try another simulation. ... We could do something extremely basic, a survival sim, "killing" our partners isn't forbidden but it does vastly decrease our capacity to survive.
Perhaps each of us has a skill that is needed at random intervals through the sim, so as soon as that person dies, the next time the skill comes up, it's an insta fail, (more so at the higher "waves" than early on, but it will always be a huge handicap)