I have no idea, lol. I like coming up with gimmicks, but I don't always have a story to fill it with. Perhaps it would be easier for them to be able to remember everything that happened. Then it could be in kinetic novel form from the view point of the MC as he reminisces over the previous runs as he comes across the various challenges in his final run. Or perhaps he doesn't remember, but each run leaves behind a memento which he happens upon. He doesn't realize what it is, but the readers are shown in a flashback what the memento entails. Or, or, maybe it could be a back and forth between the MC on his last run, and his friends back in the real world, as they deal with the reality of having been gone. They spend time with each other, coming to terms with what they went through, and telling the stories regarding where the MC happens to be in the form of flashbacks, and praying for the MC's safe return. Maybe the MC will somehow get to see them in his last moments (assuming he fails), and his friends will shed tiers after instinctively? becoming aware of his loss. Bit cliche and overdramatized, perhaps, but this is probably the way to go.