In most cases the release date stays intact. Being sent back from a therapeutic community to a standard facility for not completing a class is a program failure, but it does not automatically alter the underlying sentence calculation.
The release date is set by the sentence itself, the good time calculation, and any applicable credits. A program requirement that was not completed can affect eligibility for certain early release benefits, but the base release date tied to the sentence typically holds.
The exception worth being aware of is if the class he did not complete was specifically tied to a sentence reduction benefit. In the federal system for example, failing to complete RDAP eliminates the time reduction that came with it, which does move the release date. If his TPM date in June is connected to a completion requirement for that specific program, the failure to finish could affect that timeline.
Without knowing what the class was and how it was tied to his sentence or release conditions, it is hard to say definitively. His case manager at the new facility is the right person to ask. They can pull up his file, confirm whether the incomplete program affects his release calculation, and give him a clear answer on where his TPM date stands.
He should ask that question directly and get the answer in writing if possible. Knowing exactly where things stand before June is better than finding out something changed at the last minute.