Unfortunately, there is not an easy answer to your question, which is why you haven't received a definite answer as to what will happen to him. However, I will try to assist and hopefully make the picture clearer for you. The first question that needs answering is what is the original charge that he was placed on probation for and what is the maximum sentence for that charge. That would give you at least the worse case scenario. Now, as to what he has been doing for the past five years, like getting is life together, improving it, and making something of himself, that is all well and good, but there is a problem. Typically, a judge doesn't really care what a probationer has been doing while in violation status of probation. Its almost like time stops when the person leaves, the term is actually absconds, and does not report to probation. However, there are many parts of this complex puzzle that would suggest what type of sentence he will receive. Here a few to consider:
1) Criminal History
2) Severity of Offense, i.e. Misdemeanor, Felony (In your boyfriend's situation, extradition usually means Felony).
3) Type of Jurisdiction - Conservative, Liberal, Student Friendly, etc.
4) Who is the Judge? What is that Judge's typical sentences?
5) Who is the prosecutor? How hard will they prosecute your boyfriend?
6) Does you boyfriend have a good attorney?
These are some of the considerations and questions that would need to be answered to then possibly answer your question. The best person to answer a question like this is to obtain the services of local counsel where your boyfriend is charged. Ultimately, that person would have the best ball park figure as to what your boyfriend is looking at. The one thing that is certain here is that if after five years they extradited him from one state to the other, then the offense is serious. Also, violations of probation are at the top of the severity charts, especially absconding from probation, because the person is showing that they cannot be trusted out in the community. So, that usually equals jail/prison time depending on the factors I mentioned above.