Not long after he's helped back into bed, he simply falls asleep and... doesn't wake back up. Coma, then death, it's how monsters tend to go.

So, not long after that, he's nothing but dust. (Pity he hadn't told anyone what he wants done with it. Nothing, perhaps.)

And when he comes back... he winds up in the exact same spot he first appeared in, months ago, under a tree near a swing Frisk built for other kids to play on.

He's no longer a skeleton. Good to know he won't become ill a second time. Disappointing all the same, to be a useless gelatinous mess.