There is a wide variety of things that can happen. The judge will take into account:
your husband's criminal
did he commit any other crimes since he was on probation
the reason that he was gone for four years
what aspects of probation were NOT completed
The judge has the discretion to re-sentence
your husband to jail and close out the file. The judge can extend probation, give your husband new conditions, and see if he follows them. The judge can extend probation but order a little bit of jail up front.
As you can see, the judge has a lot of discretion depending upon the different variables.
From the facts that you described, I hate to suggest it, but no one should be surprised if your husband is sentenced to some jail with the file closed out.
Basically, at the hearing, your husband needs to explain to the judge why jail is the answer and it better be a pretty darn good reason.
If your husband hasn't done so already, he may want to hire an attorney to help him in this process.
Good luck and best wishes! I hope that you find this information to be helpful and this answer to be ACCEPTable!