Everybody who says there's nothing wrong with him is kidding himself. We've all seen the decline for years. After the 2003 crash, it was never the same again, but unfortunately, there's not a thing anybody can do about it. I think the 2005 tour was still on guitar hero level, but you can't deny guitar-heavy songs like Sultans and TR being significantly sloppier from the 2008 tour and onwards. One of Mark's strengths is accepting and adjusting to circumstances. Setlist controversy and comfort-zone discussion aside, he's made most of the remaining touring years since then.
Of course, most players get worse as they age and the years go by. However, the difference between 2015 and 2019 was night and day. Though I enjoyed the last tour, it was clear from the first night that it would be the final run. It really breaks my heart to see him struggle to play four notes that he's played hundreds of times. I strongly believe we won't see him doing any promo, let alone gigs. We should be glad with the tours he's given us, and visiting Christie's in London was a wonderful surprise, even providing some closure for me.
Edit: I hope I didn't give the impression that I want to speculate about health details. Quite the opposite, I'm not interested in that, and it's also not anyone's business. I just wanted to point out that it's obvious why he won't play anymore, and it might very well be also one of the reasons to sell so many guitars.
