In something more prone to failure but easier to imagine for some, imagine they are sealed boxes, each containing a few thousand unique people having different and meaningful fun together for eternity.

Thanks, this is better.

One approach would be to figure out the magnitude of the implicit risks that I take all the time. E.g. if a friend offers me a car ride that will save me 15 minutes over taking a train, I tend to take the offer, even though death rates in car rides are larger than in regional trains. While I don't assign death infinite or even maximal negative value (there are obviously many things that would be worse than death), I would very much prefer to avoid it. Whatever the exact probability is for the chance of dying when taking a car, it's low enough that it meets some cognitive cutoff for "irrelevant". I would then pick the N that gives the highest expected value while without having a probability low enough that I would ignore it when assessing the risks of every-day life.

I'm not sure of how good this approach is, but at least it's consistent.