In my interpretation of the Giver, Jonas is still alive after the ending. In my eyes Jonas seeing the house was basically the memory of that leaving him as he left the farthest boundary from the community. When he fainted or closed his eyes he was fainting because of the lost memory. A little while later, a group of natives(or Indians) had found Gabe and Jonas. They then took the two children into their village. Jonas after re-awakening, had such a big chunk of memory lost that all of his memory was lost. Gabe just grew up from then on. It may sound a little far fetched but i still belive that Jonas and Gabe are alive.
http://www.goodreads.com/interviews/show/813.Lois_Lowry
http://www.scholastic.com/teachers/article/lois-lowry-interview-transcript