Disabling stylesheet, as you’d expect, though, completely breaks things. Progressive enhancement, or at least graceful degradation would be nice there, since this can help with assistive technologies. This could go hand in hand with the proposed basic HTML view mentioned in Discourse will be dropping IE9 support in 2016
(I don’t really expect disabling to be a supported case, I just mentioned it because its something a user might try to get over an accessibility problem with a site.)