As a former Guardsman, I always thought the story was silly. Gaps in service happen all the time in the Guard, especially when someone’s day job requires time away from the home drilling station. It’s no big deal — certainly not enough to be considered AWOL by any stretch.
One aspect not often discussed is W’s fighter jet was being phased out. I think it was an F 101 or F 100. To move into a new airplane would have meant several years of additional training, which would have greatly exceeded his time left in the guard.