I can't imagine my family being "crushed" with disappointment if a military family member couldn't make it home for the actual holiday.
I think my own mother would rather know, and she'd be able to handle the "if the Army comes through" idea. And if it turned out that the leave was cancelled, I think she would have liked knowing that the child in question had really *wanted* to come home and had tried.
Maybe other families don't do well in a changeable world, but mine does.