If his probation is revoked, he may very well be looking at completing the full sentence of his underlying charge. Many people think that if revoked, a person just has to complete the remainder of time left on probation, but that isn't true. For instance, if he had a 5 year suspended sentence and put on probation, then he would be looking at going to prison for the 5 year sentence.
He could also get a lesser time, or be ordered to go to a half-way house or something like that.
There is also a possibility, of course, that they will just let it go and put him back on probation.
What happens depends on his other criminal history, his work history, the court's intentions, and other things.
I wish I could be more specific, but sometimes people who have a terrible record, history of problems and everything else, get out of trouble on their probation revocation. Other times, for the least little thing, the court throws the book at them.
He should prepare his best presentation to the judge about how well he is doing and how he has turned his life around. I wish him the best.