I am so sorry you have to go through this! I will do my best to aid you!
Crested Geckos can tolerate higher temps then most people give them credit. But over 85°F for an extended period of time is pushing it.
First, figure out the coolest part of your house and temporarily move the tank there. You may want to start freezing water bottles right now, those can be put on top of the tank (Lid) and around it. After the power goes out and the ice melts you will just have to do your best with other things. Basements tend to be cooler so try to find some place like this to move your Crestie. Make a little "sauna" (Plastic deli-cup or sandwhich container with airholes, spray the inside generously.) and provide it in the tank, make sure you keep up with mistings as well. Dehydration is very deadly.
If things get very hot, move your gecko into a temporary container inside cooler (Foam ones work well) that has holes to breathe. Mist very well.
I suggest you freeze bottled water, ice cube trays, etc. Whatever you will need to keep things cool NOW. When the power goes out immediately put those things to use and store them in any insulated cups/coolers you have.
You be safe too!