July 8, 2013. After arriving at YYZ from LHR, it was raining like I've never seen. We were stuck on the tarmac with at least 40 other planes for an hour before we were able to get to the gate.
I had received text messages when I landed asking where I was and that there was massive flooding along all the major highway arteries in and around Toronto. I was told not to attempt getting to downtown and that the power was literally out throughout the entire region.
So I immediately booked a room at the Westin Bristol Place (now called "The Westin Toronto Airport"), which miraculously had availability given all the IRROPs that day.
The hotel shuttle was packed and standing room only... I was the last one on and was standing on the top step that leads to the main passenger door.
When we got to the hotel, the lobby was lit with candles and there was minimal power on with backup generators. The lineup to check-in was roughly 100-people long, but luckily as a Starwood Platinum I was allowed to check-in right away. Everything was done manually by the front desk. Only the elevators, the room doors, and hallway lighting worked. We were warned that there was no electricity or water.
I got to my room and it was pitch black. I had to use my phone light to get around the room.
The next morning, with my breakfast voucher, I went downstairs to see if they had anything at all to eat. Luckily it was continental breakfast with everything sitting in ice from overnight. The power was still out.

Overall, it was an uneventful stay and I certainly didn't ask for any compensation, given the magnitude of the situation which is now referred to as The Toronto Flood of 2013.

PSA - CPAP power options
 

I travel around less developed countries and I have a battery powered CPAP that can run for two night on a full charge (Z1).
As most of the latest CPAP units run off a powerbrick there are many inline battery backup options that keep the machine running when power is out.

Every chain hotel in the United States will have emergency lighting. That will be a basic requirement in order to get a franchise in any hotel group. But, battery back-ups don't last forever. I wouldn't be surprised to see those hallway emergency lights start failing reasonably quickly. They are there to aid people in an evacuation, not to keep the hotel habitable.

I lived in a mid-rise apartment building when Hurricane Wilma came through South Florida. We were without power for 22 days. I don't recall how long the emergency lights lasted, but it wasn't long.

At some point, a building without power should get evacuated by local emergency officials. But, there needs to be someplace to put people, too. The apartment managers told us we had to leave but they didn't force us because there was nowhere to go. Hurricane Wilma was about 6 weeks after Hurricane Katrina and a month after Hurricane Rita. So, people here just managed the best we could because other places were far worse off. Any other year, we'd have probably been relocated, courtesy of FEMA.

While it may not seem like the hotel was going to do anything, you may not have been privy to all the conversations. Was this power outage just at your hotel or were big blocks of the city impacted? Sometimes you just have to take a wait and see attitude. If the accommodations weren't going to meet your needs then you had every right to check out (with a refund of that night and remaining nights) to find another hotel. It is a big undertaking (not to mention expensive) to move an entire hotel worth of guests to neighboring hotels which may or may not have the same problem.

To answer your question, would I be HAPPY about it? No, I wouldn't be happy about it but I would play the situation by ear based on surrounding conditions and other options. If it was 100 degrees and I was on the 15th floor and the hotel down the street was operating with no issues and they had availability then I would have moved and taken it up with corporate if the hotel was refusing assistance. My other big caveat would be if I was on firm business. If the extended outage was somehow going to impact my work schedule then I would just have moved, charged it to the firm and moved on with life,

This is definitely a situation where proactive communication from management is critical and can totally change how guests perceive the issue, even if it's a case where the whole city is without power and there isn't a lot they can actually do.

Not saying anything and looking unprepared is the wrong way to go about it.

In the case of the OP, it's possible the hotel manager knew a crew was working on the transformer and would have it up and running soon. But if so, the FDC should have had a different response...and they should have been able to answer questions about what would happen if the power didn't come back on.