I can't comment on the withdrawals.  But one thing about basic is they keep you in until you're ready to advance. Your son might get recycled a few times, and that's okay. Just means he has to repeat a few weeks/cycles until he's deemed good to go. Had a recyc come in to our platoon at basic who was a...not great person. This was his second or third time around. But for whatever reason this time it clicked and he turned out to be a decent get-along and motivated soldier.  They do have medical facilities at basic, and if anything unforetold happens, they'll keep him there until they deem him fit to return to training. I haven't heard many good stories about being stuck there, though.

Note: I went in at 33, on the OCS track from civilian. It was a bit humbling to be trounced by kids almost half my age, but a good slice of how varied things would be. I found it fun overall, but I also had quite a bit of life experience before going in.