I think that Jonas is alive because he clearly states that he wants to save Gabriel from being released. On page 180, he says that he thinks he hears music; but The Giver never gave the memory of “hearing-beyond”. It must have been an echo, not the music of angels.

With the memories that The Giver gave him (the hill and love), were probably given to Jonas to assure that he will make his journey to Elsewhere (the real world).

On page 179, Jonas said he lost consciousness, but he forced himself to stay upright. The houses of that memory connect his dream (with the snow), the snow making him to have that urge to keep sliding down the hill. Some people think he is hallucinating because he hurt his knee, and is thinking about the memory. I don’t think that because on page 93, Jonas was asked to look at the sled, there was no Gabriel with him.

Jonas had the will to live, The Giver gave him memories of courage. On page 180 he said that he was aware with certainty and joy that below, ahead, they were waiting for him, and the baby. “They” could be another community waiting for Jonas.

In conclusion I think Jonas is alive!