This isn't really enough information to be definitive. A petition to revoke is the paperwork filed in court alleging someone has violated the rules of probation. Without knowing the rules and the violation it is hard to predict.
All violations, however technical in nature, can subject you to facing resentencing under the guidelines of the original charge as all violations equally violate the sentence. You may have a hearing to determine if you violated the sentence, and the state must prove the violation was willful on the defendant’s part. This proof is not required to be beyond a reasonable doubt, as is a trial, because the defendant carries no presumption of innocence. At this hearing the proof must be by a preponderance of the evidence only (essentially that it is more likely than not the violation occurred willfully).
If the determination is made at hearing or after admission the defendant violated the sentence, the defendant is resentenced. This is where differences in violations come into play. For instance, commission of the same crime again is treated more harshly than say, missing a night of curfew. This is a generalization but it is a good one. Everyone should note that there is no set guideline in the law about the value of any given violation.
This sentencing does open you up to getting the maximum, but the truth is that the majority of violations I have handled over the years result in a continuation of probation and some punishment (such as more jail or public service) or additional services (like additional counseling or drug testing). Every case is different, just like each violation is different, but few people are sentenced to the maximum penalties for an offense after a single or first violation.
It is the overall exposure which makes me urge people to seek counsel for violations. It should be treated as carefully if not more than the original charges in court. You have the very right to counsel at the violation hearing and sentencing you did prior to trial or plea on the case, and you should take advantage of this right.
Please understand that answering this doesn’t create an attorney/client relationship between us, and as hard as I try to answer your question well, it isn’t legal advice. No matter how much information you put into a question, the answers you are going to get are still going to be vague. It is in your interest to contact a lawyer, most of whom will do a free consultation. Even 15 minutes with a lawyer is going to produce a more specific answer to your problem.
Your question is extremely open-ended. To adequately address your concerns, I would need the charge for which he received probation, the Court that sentenced him, and the terms of the petition to revoke. Your friend will need to appear on the petition to revoke, either acknowledge that he violated or proceed to a hearing to determine if he violated, AND then if found in violation be resentenced on crime for which he is on probation. Normally, having experienced counsel assist him makes a difference. Please feel free to call.