What does the United States military gain by doing this, exactly?
You can't just wander off with no reason when you're in the military. And, the military is kind of a stickler for rules and discipline for whatever reason.
It's just that getting held captive by the Taliban for four or five years or so would fit most people's definitions of 'having suffered enough' and then some.
Perhaps they could charge him and have him answer for it and then commute any penalty as time served.
I can't tell whether you're seriously suggesting this or not, but I think that isn't a bad idea at all, actually.
It sounds like this is exactly what could happen in terms of avoiding any jail time, but there will still be a monetary penalty re: not getting back pay:
http://www.nbcnews.com/news/us-news/bowe-bergdahl-likely-be-charged-desertion-officials-say-n294466
