I see a lot of problems going on here, and they mainly have to do with the DM not keeping his game under control. I won't go into that. I don't think it's necessary.
But you did say he is 19th-level right? Mordenkainen's disjunction is par for the course. It's part of the game. Use it. If your players aren't mature enough to handle it then tell them they don't deserve to play high level characters and start a new campaign at level 1.
I once ran a campaign from 1st level all the way to 22nd. I used Mordenkainen's disjunction twice among other terrible things you encounter at high/epic levels and don't regret it. People need to get over the idea that once you have a magic item or special power it should be yours forever.
I offer as a little story a tale about a wizard known only to the world as EC. EC was a great wizard, enormously powerful, but one day through a series of unfortunate events he was forced into a demiplane where magic did not function and he was forced to adapt. He became a fighter, and a pretty darn good one at that. He became adept with using two weapons at once, which was a coveted skill in his time, and through cunning, guile, and a little bit of luck, found his way back to his home plane. Once he had returned he re-united with some of his old allies and returned to plumbing the depths of dungeons. As he continued to adventure, he achieved greater levels of power than he ever had before as a wizard. His exploits eventually brought him not one, but two vorpal blades which we wielded with extreme skill. Then one day, on an excursion into the depths of a truly ancient dungeon full of traps and intrigue, he came across an imprisoned demon that convinced him it was an angel and that it would bless him if only he released it. He and his adventuring companion were fooled by its wiles and found a way to release the demon. As the demon cackled with glee, it offered to repay EC and his companion by enslaving them forever in the depths of the Abyss. There the demon tossed his prized vorpal blades into a pit as deep as the Abyss itself where they were never heard from again. Luckily, EC did eventually manage to escape slavery at the hands of the demon, but he was forever without his mighty weapons. But he picked himself up, dusted off his breeches, and (saying a quick curse to his deity who had done nothing to help him) began to adventure again. His experiences had made him all the wiser.
EC was a character in Gary Gygax's Castle Greyhawk campaign many years ago. EC stood for Erac's Cousin and was a character played by none other than Ernie Gygax, Gary's son. The moral of the story is that even the best DMs among us realize sometimes that we have let our player characters go too far and must reign them in through drastic means. It is the responsibility of the players (like Ernie) to be good sports, be happy about getting to be the bee's knees while it lasted, and start adventuring again for the next great thing.