Then the short answer would be "yes." Until a student graduates with a regular diploma or until the student turns 22, IEPs are in force.
HOWEVER, placement is determined by the IEP Committee. If the IEP Committee/Team (parents and educators) have placed the student in Adult Ed, then the IEP must be followed in my opinion. It would be no different than changing placement to self-contained classroom from mainstream, mainstream to theraputic day school, etc.
Sounds like someone, parent and/or student, may need to call an IEP meeting. (I wouldn't expect behavior interventions would be included in an adult setting, however, modifications,tutoring, etc., might be appropriate expectations to get written into the IEP.)