The Royals will politely dine with him and pose for photographs and be disgustingly cordial. No one in power (or implied power) has the balls to stand up to this prick.
Alas you are probably right. That said, don't rule out a Trump gaff that has Prince Philip exploding on him. Philip's never given a shit what anybody ever thought or said about him, and he's so ancient now his field of fucks is probably about as barren as the Sahara in high summer.
I really hope against hope that the Queen gets some sly digs in, but Trump probably isn't smart enough to get them. He might have a bust of Churchill in the WH - the Queen
knew Churchill for more than 20 years; he was her first PM. She's known presidents all the way back to FDR most likely and will be well aware what a political pygmy Trump is by comparison.
There's all kinds of shit she could politely throw his way and he wont get it at the time, but it would come out soon enough and he would realise he'd been taken for a fool.