I think Jonas is alive because he didn’t take pills for his stirrings so all of this might be just a dream. Also if it was actually happening he wouldn’t have taken Gabe to Elsewhere if it was heaven. Jonas loved Gabe so much that he wouldn’t risk Gabe’s life. If Jonas was dead all of his memories will be released to the community but he could still share the memory of warmth with Gabriel, so I think Jonas is not dead.

The Giver told Jonas that he had the ability to see beyond so maybe when Jonas felt he reached his destination I think he saw beyond his future of finding a new community that was the Elsewhere The Giver and Jonas thought existed. After they ran out of food Jonas thought they would starve to death, but he loved Gabriel so much he didn’t want to give up and he had the will to live. Also his mind was alerted when he felt like he found the Elsewhere, if he was dead he wouldn’t feel anything.