What happens to Jonas & Gabe at the end of the story?

That's your choice.

There are
many ways what happened to Jonas and Gabe. The last thing that happens it that they ge
on the sled and go down the hill. It says in the book that Jonas can feel warmth near
his feet. As he goes down the hill, he can hear music. He knows his close to
'Elsewhere'. So teh story can end that he went ot another Scoiety that doesn't have the
Utopian society in it.

Or, logically, they can't really
stay in teh snow for that long and also when Jonas is transmitting Memory of Snow to him
and they do become cold. They run out of food, and personally, i would die in that
condition. The story can also end for them both dying for hunger, weakness and
coldness.