Except (may be wrong) some folks could be injured in their first week of deployment and not qualify for the medal. Or would they make an exception. Just getting the clasp wouldn't be very good. I suppose it simply depends upon writing the criteria correctly.
I think the point was covered earlier in the thread, but to confirm, the full qualifying period is not required if the qualifying service is brought to an end by death, wounding or other disability due to operational service.
That's from the criteria for the Iraq Medal (Op TELIC). I think you will find similar criteria for other campaign medals.