Despite his legal credentials, Dershowitz has a poor track record as prognosticator.
This is just pure punditry... your prediction is as good as his, because no one knows what the hell is going to happen here. If there were any defendant other than Trump - yes, the conviction would be overturned in a heartbeat. It would be one of those cases so egregious that the appellate justices ruled from the bench rather than wait for a written opinion.