Ending
They died. At least that's what I like to imagine.
Because not only was the ending really bad, apart from still a few laughs, but Jane's appearance was really badly written and unrealistic. My view is that the final scenes we saw, were all from each of their minds as they died and imagined being rescued.
Jay. Jane didn't know Jay was there, and hardly seemed surprised to see him. No, "oh my god. Jay! And you guys! What on Earth are you doing here?" And Jay then confesses his love. But she didn't seem to really care that he was out here. It was like seeing a drunk friend in a street who you see every day and then helping them up and taking them back home.
Will. Gilbert turning out to be the one who Will's mom is actually seeing. That would be a nightmare, and he even mentions is he dead and living in Hell.
Simon. Lucy breaks up with him, which is what he would want as he still finds it hard to break up with her.
Neil. Well, Neil got the attractive elder lady again, and had the most 'happy' thought.
And the bits of them travelling are all part of them being friends again, and happy to travel with each other. You could say if they were dying they would see good things, and not chick with dicks in Thailand, but they just wanted to be rescued. They all thought of Jane rescuing them, and the possibilities afterwards. And as he knows he is dying, he thinks about who it could be who his mom was, and it is his worst fear is Mr Gilbert becoming his step-dad.