Since the person you are talking about is on a deferred adjudication for what appears (by your description) to be a State Jail Felony, the Judge of the court has a lot of discretion over what he can do with him for sentencing him. Legally, the Judge COULD reinstate him, if he or she wanted to. THey could also sentence him to anywhere between six months in State Jail to Two Years.
It all depends on the Judge. He definitely needs a lawyer.
In addition to the above answer, why he left and what he's been doing since he checked out are going to be very important. If he's working hard and staying clean, that's in his favor. If he's not working and using/drinking that will not bode well for him at all.
He needs an attorney to help avoid being revoked and adjudicated.
Although my intent in answering this question is to aid you in the legal process, my answer does not establish an attorney-client relationship in any way. You should seek the advice and counsel of a qualified attorney in your community to evaluate your legal needs and to advise you. No Attorney-Client Relationship is created without the specific intent of both parties.
Most defendants do not receive the maximum if they are revoked unless they have been charged with a subsequent felony offense. There is no incentive to agree to the maximum term. Just as in any plea bargain, any jail sentence would likely be less than the maximum. Some judges will convert a deferred into a regular probation and restart the probation period. This results in a conviction plus the judge has the chance to keep the under supervision.