This sucks..

Exposures to temperatures below 72 degrees for extended periods of time will, IME, almost invariably result in an outbreak of ich. This would be a particular concern with a fish such as a regal tang, which is already highly susceptible. I would prepare to deal with ich, and, as soon as the regal is looking a little less stressed / more stable, I'd isolate him into a qt tank if you have one, so that you can treat him as necessary.

Sounds like you're on top of things, then

Watch for any cloudiness and test the tank regularly as you will more than like run into a bit of die off of the microbial types. this is very probable if you have any LR in the tank so you should be ready to do some water changes as well.

Just to clarify something here--ich is NOT present in all tanks all the time, and must be introduced to an aquarium. If the parasite is not present, no amount of temperature changes or other stressors will cause an outbreak.

Otherwise, monitor for ammonia, and be ready to do water changes.

Yeah, I agree with OrionGirl on this one. If you haven't seen ich in the tank recently, it's probably not there. Nitogen from die-off is probably the big issue.

On the other hand, if you do see any signs of cryptocaryon, it will support my theory that you can have apparently healthy carriers in the tank for extended periods of time.

I've talked about this on other boards, but for how much $$$ we all have invested in our tanks, EVERYONE needs a generator just in case some type of disaster should happen...

Even if you only spend $300 on one of those loud contractor units, you only have to run it in little steps to keep the tank up, put a long extention cord on it and you're set..

plus your neighbors will want to leach power off of you also so it can be a good thing...

or spend some more $$$ and get a quite Yamaha or Honda that can run 5ft. away and still talk at a normal level..

I myself have the new Honda 1000u which will run everything I need, plus the big unit in the Motorhome incase I need big power...

but Since I'm in Cali, usually we only loose power usually when we lose our homes so there's no tank to worry about anyways

But we've been without power for 13hrs. before a gen. saved my parents tank..

We got a 5500W unit after Isabel, and I have had no regrets. Not just the peace of mind about the fish and corals, but also about the fridge, etc. We have outages every time someone sneezes, so it has been getting a lot of use.