Re: A potentially bad problem for my 6800 GT.
What was the temperature threshold on 6800's again? 110 or thereabouts? 90 really isn't that bad, I've seen far far worse. A friend of mine had two 6600gt's in SLI, and the bottom card (ie; egg-fryer) was sitting at an average of about 85 degrees (celsius) for probably a good two weeks in his cramed little case. It still works just fine to this day, they're a tough series of cards those, and I'm sure you have nothing to worry about. With a stopped fan, I would've expected temperatures well over a hundred, so the air moving over the heatsink couldn't have been too bad (remember, opening your case and feeling the flow from that fan you mention isn't entirely accurate - with the side panel on, airflow is drastically altered, and likely improved).
Fingers crossed, sure, but I see no reason for it to fail. Be optimistic!
Q6600 G0 @ 3.42ghz
8gb Corsair Something-o-rather
Soundblaster X-Fi XtremeMusic
850w Antec TruePower Quattro