If a god descended from the heavens and spoke to you, personally, declaring existence and providing myriad demonstrations of divine power, I expect you would reconsider your belief at least a little bit.
Given what you already know about the world (including the possibility of insanity and simulations), how much evidence should be necessary to convince you in that situation? A subjective year? One hundred? One thousand? More? Once you've already decided that you're insane or in a simulation with probability X, I can't see how any evidence of anything would be useful if you already assign less than probability X to that thing. It's a local minima you can't escape from as far as I can see. One reason I'm not especially anti-religion is that I think that at least some theists are in the same position: there's no evidence that is more likely to be real evidence that there is no god than it is to be evidence of testing by fallen angels, or whatever.
But maybe I've just missed the excellent discussion about this?
Followup to: The Strangest Thing An AI Could Tell You
Brain damage patients with anosognosia are incapable of considering, noticing, admitting, or realizing even after being argued with, that their left arm, left leg, or left side of the body, is paralyzed. Again I'll quote Yvain's summary:
A brief search didn't turn up a base-rate frequency in the population for left-arm paralysis with anosognosia, but let's say the base rate is 1 in 10,000,000 individuals (so around 670 individuals worldwide).
Supposing this to be the prior, what is your estimated probability that your left arm is currently paralyzed?
Added: This interests me because it seems to be a special case of the same general issue discussed in The Modesty Argument and Robin's reply Sleepy Fools - when pathological minds roughly similar to yours update based on fabricated evidence to conclude they are not pathological, under what circumstances can you update on different-seeming evidence to conclude that you are not pathological?