Well, if this is deliberate, it supports my feeling that there are some faintly religious undertones throughout the whole Uncle Harold episode. Uncle Harold -- or "herald," a harbinger or announcer -- may or may not die. Jack has no control over it, either from "up here," in their Brokeback Eden, or "down there" in worldly society. Not long after that, Uncle Harold is resurrected -- that is, he doesn't die, even though Jack didn't go see him. And that news is of such primary importance that Jack announces it to Ennis even before explaining that their mountain idyll is over.
What does it all mean? I'm not sure. I don't think it fits together into a neat package. But combined with the parallels in the post-divorce scene (an unexpected arrival announced with "here I am," someone peering off into the distance, Jack following the person's gaze and coming to a realization, a choice between between romantic love and family commitments -- Jack deciding one way and Ennis the other -- the prospect of being seen by the outside world, Uncle Harold's survival and Jack's figurative -- and eventually literal -- "death," both Uncle Harold's and Jack's involving fluid in the lungs), it seems to have something to do with being powerless to control fate through one's actions. Jack can't save Uncle Harold by "rejecting" Ennis, so he doesn't try, yet Uncle Harold survives anyway. Ennis thinks he can save them both by rejecting Jack, so he does, yet Jack does not survive anyway.
Does that make any sense?