If the appellate court sends this back to the trial court, and he prevails, the conviction will be vacated. He could then, in my understanding, negotiate a plea in order to avoid a second trial. I don’t believe the state would offer him less than the sentence he is already serving, which is the mandatory sentence for murder, unless he cooperates and offers them something.
So, in response to your question, it is my understanding that the deal could only come after the conviction was already vacated. If he were to renege, he wouldn’t get whatever they offered him.
I don’t think the state could offer him a deal prior to the conviction being vacated. Right now, the appellate court has jurisdiction, and the state attorneys cannot do anything in the case at all. If the appellate court gives up that jurisdiction, it would only be for the limited purpose of getting the trial court to have a hearing on the issue of the conflict. If the court decides the conflict didn’t give him a fair trial, the conviction will be vacated, and only then can the state court get jurisdiction back completely and potentially make a deal.