He was dead before she let him go, he died of hypothermia, hense when she lets him go she says weakly;
"I'll never let go, Jack." It was a promise she made to him and she felt she owed it to him to survive because in those fateful moments he says to her;
"Don't you say that, don't you say your goodbyes.
Your going to go on and live an old lady and
die warm in your bed, not like this, not this night."
I'm getting emotional thinking about it, it's so very sad
.