Short Answer:
"Dogs and cats living together. Mass hysteria!"
Longer Answer:
Some older gamers move away to nostalgia games (OSR) or stuff promoted on old-school social media like YouTube (MCDM). Some stick to 2014 or go back to Pathfinder or 4e (like me). We introduce our players to different game systems and they don't buy into the 2024 printings - and let's be honest, they weren't the market drivers anyway.
Put this way, I GM for 11 players on a weekly basis. I purchase more content than all of them combined. Hasbro has essentially lost me as a customer - so that's 12 customers they lost. I'm not going to be running their games at conventions, game stores, programming at work, etc.
Most Longest Answer:
Nerd culture is going to retreat into the background in the next several years. No, not just because of D&D, but I think it will happen. Game of Thrones has been forgotten. Stranger Things is wrapping up this season. Superhero films have stopped rocking the box office. Comics have been dead for years. The one thing still selling is a direct competitor to D&D - and that's video games.
So we're going to see what happened during the 4e era. We're going to start losing players to Baldur's Gate and other video games just like we lost to WoW. The booming success of 5e was a fluke, and most of the players who came in are going to fade to other hobbies or adult responsibilities. Hasbro might retain 10% of the new fans they gained over the past 5 years. This will probably mean that WotC doesn't generate the income it needs to, Hasbro continues to suffer financially, and likely ends up bankrupt in the next year or so.