What are his chances of going to jail?

A friend of mine has an adult son who is an alcoholic, and also has mental problems. When he drinks he is like a small child, playing pranks and doing other mischievous actions. I sometimes wonder if he is retarded. A few weeks ago he was arrested for waiving a fake knife in public. Of course, he was drunk and thought he was funny. The police didn't think so. On the court date, he arrives drunk and is not allowed into the building. A warrant was issued for his arrest. He was able to talk to a public defendant who told him to see him the next day because he would be able to get the warrant squashed. When he arrives the warrant is squashed but he was given the option of spending 40 days in the county jail or go to trial. He chose to go to trial. The trial date is approaching and he is almost sure that he will go to jail. I would like to know what his chances are. Because of all his handicaps he has never been able to keep a job for long. His mother supports him financially. Neither one can afford to hire a lawyer. I am concerned because I have known him since he was in kindergarten and wouldn't want him to end up in jail. He is not a violent person at all, even when drunk.