I don't think Michael was afraid of this sort of therapy. He was probably more afraid that Terri might improve if given such exotic treatments as being taken out in the sunshine, having a fluffy little kitten nuzzle up to her, or generally treated like a human being. Any improvement resulting from that sort of treatment would have been a stronger indictment against Michael than a full recovery resulting from a treatment that had not been previously available. Even if Terri remembered the attack, it would have been very easy for Michael's lawyers to claim that the memories were false and had been implanted by her caregivers.
On the other hand, if she had improved when given sunshine, etc. that would have proven that Michael had been sandbagging her condition for the purpose of killing her. And he'd really have no defense on that one.
I think he was afraid she would make a come back. I think he was responsible for her condition.