What exactly did the lupus do? Was it just the singing? It's a difficult situation because even at 50, many people expected to be this incredible, agile dancer when he naturally couldn't be.
I think in that case, he should adapt to the situation and switch things up with his show, dance less routines but sing more. Hell, maybe even learn to play guitar for a couple of songs and give a bit of an unplugged performance... it's not his usual style but it would switch things up! He's known as a dancer too so he could still have small concentrated bursts of phenomenal dancing, and if he was really worried about being visually interesting, he could probably get more theatrical too but even when it's just him singing he can be so great to watch. What comes to mind is a clip where he actually is just singing Earth Song live, and it's just incredible.
Great singers can still be captivating even if they're not dancing around, Michael certainly could be. I mean that's just probably what I would do, maybe I'm being overly hopeful but hey