How likely is it that a court appeal would be successful?

Does he have any prior convictions?

Hard to tell.

Would need to know details of the conviction, and read the motion for appeal.

The DIstrict Attorney could offer an expert opinion to you, if you ask.

We don’t know the case and there is no way to have an opinion about it. There could be a technical reason the others were dismissed that doesn’t apply to the one he is convicted of.

Only about 20 percent of criminal appeals are successful. But the odds of success are much greater if there were errors of law and procedure at trial significant enough to have affected the outcome of the case.

Your best course is to talk with the DA. They are more than willing to discuss the case with those impacted. Even if you aren’t a direct victim or something like that, they would likely discuss the general topics such as how strong the appeal is, etc.