Explaining the ending [SPOILERS]

This is a piece of art where the ending depends on the perspective of the viewer. Writer/director Sayles said he tried it both ways and neither was satisfactory, so he left it open.

The three options for the viewer come down to the three protagonists: Joe was a realist, Donna an optimist and Noelle a pessimist. Donna and Noelle were opposites while Joe perfectly fit in the middle. You could say the three worked together & belonged together like a 3-strand cord.

Jack knows it's not really Joe's fault that his sibling perished; Joe himself barely survived, not to mention lost everything and now barely gets by. So there's nothing to resent. Wanting to remain in Alaska, Jack flies back and tells the drug dealers he saw no signs of anyone surviving, which would satisfy the thugs and they'd depart. Jack could then report them to the authorities; but whether he does so or not, he'd either go back to pick up the trio after the storm or have the Coast Guard do it with his assistance. According to this interpretation, Donna was right about Jack when she said she looked into his eyes and knew he was a noble person, not a lowlife killer. If there was any selfish motivation, it would be Jack's desire to be recognized as a local hero with word spreading in the bars & community.

In a way, it doesn't matter: Donna and Joe finally found the right mate after a lifetime of searching -- a person they could be in the worst possible situation with and it didn't negatively affect their relationship. Furthermore, Noelle needed a father figure and Joe unhesitatingly said that she could stay with him. Remember, he never had a child, but now he has one; he thus viewed Noelle as sort of a treasure thrown into his lap. Also, factor in how both Donna and Noelle liked Joe before either knew the other knew him. In other words, both had good vibes about him and this never happened before in their relationship concerning Donna's romantic partners.

As such, even if the plane landed and someone in the plane shot them all while they're arm-and-arm on the shore, it didn't matter -- they would pass into eternity with their closest loved ones.