My friend is on probation for fel drug charge, he was arrested last night for DWI... what will happen?

he is real close to being done with his probation time, however, he had a few mess ups at the beginning of his probation (failed UA) but he got back on track and has done very good, not missed a meeting, payment, etc. and then last night he had a few drinks after working for almost 36 hours straight, he was tired and knew he didn't need to drive so he pulled off the side of the road, put truck in park and leaned his seat back and was gonna sleep a while before he drove anymore. a cop pulled up after he was asleep, woke him up asked him to get out and do field sobriety tests, he complied, but refused to blow so he was arrested and taken to jail for DWI. what will happen to him? will his probation be revoked and he have to serve prison/jail time? I'm worried.