Imo mid majors will come down from their golden age for a while. But I don't think they're dead. Actually, now that so many P5 schools have the chops to get largely Calipari-type players, I expect P5 schools in general to follow something like a Calipari story arc. Especially the schools who are most successful in this new landscape. I expect they'll reign practically unchallenged for a while, but then get complacent as a result of being able to force Ws through on size and talent alone.
Meanwhile less wealthy schools, especially mid majors, will be struggling to perfect their offenses and defenses enough to compensate for all that firepower. As a result, the most radical and effective new ideas will be picked up and perfected in those schools long before the star-packed schools, which will still be able to muscle through without them. Then in some senses the whole P5 pack will be the new post-'19 Calipari and the mid majors will see their star rise again for a while.
All complete conjecture on my part. But it's based on real factors that I don't think anyone can wish away. Now that I think about it, it all runs pretty parallel to Asimov's Foundation, which, I guess that's an AppleTV show now but I have no idea if they're telling it there in a way that fits this picture, which the books definitely did.