Interesting point. Though I think it's more possible that it's a reason for them to be so friendly with each other (even though these strings are not visible to them as they are to us, readers) than a plot-device to make the story progress.
Well, this is a possibility that we can't ignore.
Still it's true that Gon and Killua already went through desperate situations, and Gon already risked to lose his life, as well as Killua back to the Chimera ants arc.
It's a possibility, indeed. But I doubt Togashi goes to that place anyway. I know He has the fame of killing a lot of characters, but He doesn't escape from the Main Character Shield that wont allow to kill the four.
The Sky is pouring
The wind is blowing
The sea looks red,
a surging sea of flames
looks like the entrance to hell
'Perfect', the captain said.