I know that Harry wasn't an academic (and no shame in that) and that it was rumoured his art teacher had to help a bit too much to get him a B at A level...
But can he really be so bone-headed to think that William or Catherine, or Anne, or Camilla, Sophie and Edward will ever want to be in the same room as him again? Surely even he can't be that deluded. Charles is his father - who no doubt is haunted by guilt about Harry's mother's life and death and is a sentimental old guy at the best of times - will feel differently. He'll be angry and very, very hurt by H & M's behaviour but he'll make up with Harry on a personal level. But I think William and Catherine would resign from the job if forced into a rapprochement with Harry and Meghan, and I wouldn't blame them. He'll get very short shrift from Anne. No-one will want to be alone with him/them again.
I guess, if the marriage fails, Harry will return at least part-time to the UK and be allowed to live privately and quietly somewhere. But he can never rejoin the RF, I think, even if he wanted to which I very much doubt. There's only a chance of a slight thaw in relationships with the family if he splits from Meghan.
Just my thoughts, before anyone dives in and asks how I KNOW this. Clearly I don't.