Good question! The answer is twofold:
1. MUDs often have a lot of text-based "graphics" such as ASCII boxes around attribute numbers and skill values. This MUD will have a screen reader mode which filters out all such things. I'm aware that screen readers already can do that, but I imagine that can still be a bit fiddly from time to time.
2. Combat will not be in real time but turn-based. Everybody will have 30 second to determine their next action, and as soon as everybody has done so the turn will be resolved and the result shown.
There's a bit more to it than that, but that's the first of it. There are more details in the first article I wrote about it which is available
$1.