Tbh it can run just fine 24/7 at 75-85c. If you have a small desktop fan you could point it at the card until you get a replacement fan for the card.
I've run a 5850 for over a year at about 82c and it's fine. 55-70 is optimal.
Would only become worried if it constantly hit 90+. That's only 'ok' for the 6990s
i wont allow it to rise above 85*c. I have not yet turned off the "failsafe" so I dont know how far it will rise past 85*c with a fan that goes to 0rpm every 10 seconds.
During the day 3 of the 4 cards get to about 83*c stable, sometimes hitting the 85*c mark. One card (best airflow) hits <80*c.
It has ran fine for a few weeks, all of the sudden the fan seems to be failing hard. Hopefully NewEgg rma will be good. I've spent a lot of money at newegg over the years, but have yet needed to RMA anything. Good experience I suppose.