Once a student has graduated or dropped out of HS, or attained the age of 21 (Martie always says 22, but I'm *still* trying to figure that one out, LOL), I don't believe IEPs apply anymore. Adult education is not required to provide the same level of supports and services that birth-21 schools are. I think the applicable law is the Adults with Disabilties Act but that only requires reasonable accommodations for a disabilty, "reasonable" being a pretty gray area.
If the student is receiving adult education as part of the transition IEP through the home SD prior to age 21/graduation, then I would think home SD would be responsible for insuring IEP issues are addressed and complied with.
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.)
A student may continue to attend school UNTIL they attain their 22nd birthday. In other words, there should be an IEP in the year the student turns 21. Typically, this only applies to severely cognitive delayed or multiply impaired kids.