Well considering that we lost a SW 46bowfront to no power for most of 3 weeks in Port Arthur with IKE 2008. And it was only 2mths along . it's always a concern for our tank here.
Our planted 50g fresh water tank made it through just find with all fish accounted for.
One of the top 10 reasons to move to Austin was no direct hit from tropical storms.
Now we have just the 44g SW. No FW tanks. We have a UPS backup unit (used for Computers) for the tank. Only the filter & power head are plugged in to the battery side. They stay on when we lose power. It will run the filter & pump for aprox 4-6 hrs. It also acts a a surge protector for large fluctuations in power...avoiding most unwanted fried filters or more in major storms.
Since our move here 1yr ago, we have lost power a few times but rarely for more than 2 hours. On those occasions the weather was much cooler so it was more a concern to keep tank warm. But something that can be remedied.
Cooling a tank can be managed carefully with floated Ice or gel packs. *suggest something sealed, that is already frozen, other than fresh water ice if you don't have a way to prevent leaks. Battery operated fans, help too.
Heating it a bit more tricky with no power. Hot water bottles for the fish...sort of. My plan was to warm water (gas stove) and float in bottles. The heat/cooling from the bottles should equalize with the rest of the tank.
If you have a HOB fliter then you can try to place teh hot/cold bottles near the outflow to attempt to maintain a consistent temp.