They normally have a lesion in v1 preventing visual information from reaching either the ventral or dorsal stream. Basically meaning that non-cortical visual systems still work, but everything in the cortex doesn't get to use it.

If the consciously accessible sections of the self-model are based in the cortex (which I think they are), then damage to v1 should prevent self-model updates.

Though, Metzinger mentions a case where someone had anosognosia for a year, then suddenly realized that they were blind.

My main (possibly only) beef with Hofstadter is the idea that the self symbol refers to itself. I currently think that it kind of does that, but in a very roundabout non-infinitely looping way.

Basically, you have all these systems that make you do things, and inputs from the body. When the doing-stuff systems make you do something, your body changes, and your self-model updates. The updated self-model is used by other parts of your brain to do more stuff, but your self-model for the most part updates after the fact.