No one will know if they trash him because no one will be watching. Look at thr level of enthusiasm for the NJ primary when Trump didn’t have a horse in the rave. No one cares. I’d say font go to the first few and let them split the vote with Desanctimonius a bit more first. Then he can jump in later to push his messaging.
People will watch, obviously more will watch if Trump attends the debate, you get out there and advocate for your positions.
Whatever the Republicans say about him, the Democrats will be just as bad if not worse.
Overall, IMO it’s a terrible idea to opt out of the debates based on the assumption the nomination is already decided,
It looks like Trump is about to be indicted a 2nd time over the classified documents issue, you can be 100% sure that will be a debate topic if the indictment happens, Trump has to answer questions about the issue, it would be much better for him to do it in a debate than having to answer the allegations on Social media or getting badgered by Reporters.