@Ren. Perhaps Puppeteer is able to accept that whether he participates or not, these people will die. Just because he is participating in the run, doesn't mean he has to be the one doing the killings. He might be opposed to what is happening but by being there, perhaps he can at least be of some assistance to the departing souls and maybe help make their transition easier and less painful. If he doesn't go, with so many people dying, there are surely going to be at least a few not able to cope with it. Angry and recently dead spirits are no laughing matter.
This is just some food for thought. It's completely up to you how you want to play through it and I will adjust the story accordingly. I much prefer a story based around the characters over characters being dragged through a story. In my runs, players are always allowed to tell a Johnson "No." without being magically forced into the run anyway. This is why I love RPGs, anything is and should be possible. Hell, for all I care you four can hijack the plane and live out mundane lives in the Caribbean. If you give me posts like "Puppeteer walks down isle 4 and browses through the watermelons." I will give you posts like "You sort through the watermelons and rap on each one lightly. (4d6.hits(5) → [1,3,4,3] = (0)) You find that they are all over ripe and unacceptable."