Weekend drills with the national guards?

i'm finding information on behalf of a friend. they are in ait training right now and was told that when he gets back he needs to do one weekend of training each month until his contract releases him. He was also told that he would be discharged as OTH if he didn't show up to those drills. my question is .. is this true? are there any consequences? i was told by a hotline that they would just discharge you by mail and they don't bother trying to track you down or arrest you unless you're of higher status and are valuable to them. can you do jailtime for not going to weekend drills? if you don't go to them will they just eventually discharge you and let it be?