The fact that there is a power outage and you're fan does not cool down the bulb properly will not damage the bulb. The only thing you need to be concerned with is if it happens often, then it will shorten the life of the bulb. How much??? It's hard to tell. As was mentioned by manpig, if it happens often, getting a backup is a good idea.
This happened the second day I had my 50V500 and I was nervous too but I feel pretty confident that when the EEs and Reliability weenies designed the TV, they took into consideration improper cool down of the bulb (ie. power outage) in calculating the MTBFs (mean time between failures) of the bulb.
Besides, I think other components are more susceptible to damage during an abrupt power outage rather than the bulb when talking critical failure.