What makes me hesitate is what was written in the screenplay: when re the shirts were what remained of the power of BBM.
But surely he would not leave Jack alone indefinitely -- there in the midst of the grieving plain...
Nice posts, Jackster, tpe, and beautifully argued, indeed, lamusica - I too have seen this: silently with her eyes and face Mom lets Ennis know (and he does pick up on it) that Ennis is welcomed to come back and get Jack and put him where his heart always was, as soon as the old bastard dies, and with as much help as Mom can give. (I've imagined them walking to that pitiful little cemetery, digging shallowly in the dry ground, Mom taking a symbolic dig or two of earth, freeing her son from his father's curse.) The shirts were the relics of the power that was Brokeback, but its power was to provide a world where they could get away from pain, fear and hate, where they could come to life, away from all their fears, obligations and expectations of misery, back to being able to care. Ennis comes all the way back from a boy whose emotions and soul were straitjacketed by the horror in his childhood to a father who can ask his own child, "Does he love you?" and know what he's talking about.
I would add even a third sobering moment in the Twist's kitchen - that look on Ennis's face when the bastard says "...and he's goin' in it." It obvious he can't believe the old shit would be that mean, but he knows enough to agree and be quiet - he's read Mom that she wants no trouble with the bastard, and Ennis complies, looking a little more sober.