Maybe nothing, maybe jail. Depends on many factors, including how busy the prosecutors are, what they think of your friend, including his attitude.
You said he submitted a dirty ua...do you mean that he knows the sample was dirty, or he was told that? Sometimes you just get lucky, but I wouldn't count on it. May wish to contact his attorney and prepare for the worst.
I'm not your attorney; my answer to your question includes assumptions. If you want me to be your attorney, I'm easy to find.
Obviously he has been violating probation by possessing and using drugs, hence the dirty UA. The probation officer's power is set by the judge. The p.o. may be able to handle this on their own, or they might have to submit the file to court. He can expect to have his conditions amended to require treatment - perhaps in-patient but at least out-patient. He can expect NA meetings. He may have his probation extended. OR, he really really really could be revoked and sent to prison. He needs to WAKE UP and cut it out or that's where he will be going.
If he is on bond probation because he is awaiting the resolution of his felony drug case, his bond could be revoked and he might be required to remain incarcerated during the pendency of his case.
If he is on probation after the completion of his case, then he could be adjudicated (if deferred) or revoked (if straight probation) or nothing or have his terms amended.
He needs an attorney if he doesn't already have one.