I think Meghan is glad to be out of the UK, glad to be away from that world and I think it would be under duress that she'd ever go back for even an appearance. She couldn't control it, she wasn't top dog, she wasn't getting what she needed, she wasn't free to be herself. I suspect she's far, far happier hawking jam to her own schedule and in her own way and of her own volition, than being managed within the RF. Sadly for her, now that she has children by Harry, she will never be able to fully shed the RF connection which I think she would dearly want (whilst keeping the titles and her DCs' birthrights, of course). The British press will see to that. She's in a prison of her own making, but at least in Montecito it's an open prison.
I think Harry MUST have some regrets. He has scant contact with his family, and it was THE royal family. For such a fragile ego as his, with as many mental health issues as he's confessed to, that alone can't be easy. And, I'm willing to believe he probably really does regret not having a relationship with his nephews and niece.