He’ll end up with years of orthodontic work to get through, I had to because I was a thumb sucker growing up. A year or so to get his bite back in the right place, then train tracks, and the rubber bands, then retainers. My teeth and bite are normal now, but I know people who have had to have their jaw broken and reset because their bite was so off from thumb sucking/ dummies. Do the kid a favour, and get rid of that dummy before he becomes far too attached to it