Research question about house floods...

OK I'm assuming the basement isn't flooded....

I would think the fuses for the power would trip and turn everything off.

Yes, they should turn off power only because they don't know not to. It is a very reasonable thing to assume it should be done. You can qualify it by acknowleding that they don't know what to do, then do it. Fuses will not just blow because of water, water would have to short between exposed live parts. Often, water is not impure enough to be a short circuit so it acts as a resistance which smolders. So be careful of those sparky scenes in the movies and tv. It doesn't happen like that.

now, a toilet flooding on the main level doesn't present as much oof a water hazard as being on the second floor. The furniture would be wet, sure but at the base only as much as it gets absorbed. I'm thinking 2 inches may not be enough to cause major flood. On the second floor, however, I can envision all kinds of dripping from the ceiling, light fixtures, walls, etc.
A leaky toilet though has me wondering why not just shut it off at the toilet valve.
A burst pipe in the attic is a classic reality. Especially up north where there are extremes in temperatures. This is a common calamity even down here in Florida (my MIL just had major flooding due to this).

So yes, turn off the power because you don't know whether you need to or not.

Question. Is the water from the tank? (clean water and the overflow was caused by a malfunctioning float valve or a broken line to the tank) OR is it a sewer back-up (close to horror movie disgusting and everything it touched has to be destroyed or disinfected)

You don't necessarily have to turn off the power, unless water has gotten in the electrical system components. If water is in light fixtures, don't turn them on.

Most modern homes have circuit breakers. The main breaker shuts off the power. Doing that while standing in water can get you killed.

If the leak is on the first floor, the water will find its way to the basement. Two inches of water on the first floor isn't likely, it would run downstairs through openings in the floor and walls too quickly. They will need to mop and maybe use a shop vac to get up as much water from the carpets as possible.

A relative had something like that happen a couple years ago. The upstairs commode was running and overflowed on the 2nd floor. It ruined carpeting in the bedroom next to the bath, then leaked into downstairs rooms, ruining the floors there also. . .not every single room, but several. I don't know how long before their adjuster came, but they rented some kind of wet vac, got up as much as they could, then had fans blowing trying to dry out the carpet, walls, etc. Ended up with new flooring anyway.

In my own experience, a nephew flushed the commode as we were leaving the house and it hung and didn't stop when refilling the tank. After being away about 4 hours we came home to about an inch of standing water in most of the house (concrete floors). It was late Friday night and my husband waited until Saturday to call the adjuster. We couldn't get him right away and we thought the carpet was a goner no matter what, so we went ahead and pulled it all up. They paid, but told us anytime that happened in future to call before ripping it out. The adjuster didn't show up until Monday anyway, so we would have been squishing around all weekend if we hadn't ripped the carpet out.

In both cases, it was something that could be stopped by turning the water off at the commode. We don't have basements in this area, so neither house had a basement. In neither case was the power turned off. If you're using a wet vac you have to have power. We hooked up in a dry area and worked into the wet. Of course, we were careful. . .we weren't running the washer/dryer or blowing our hair dry while standing in water either.

In 2 hours you might get squishy carpets and standing puddles in some rooms, but you won't have 2 inches from an overflowing toilet. You'd have to have a bigger break. . .maybe the water pipe coming up to the commode tank and it came apart at the cutoff valve so the cutoff valve doesn't work so water would be spraying everywhere? I don't know if that would work. Maybe some of the guys could tell you on that.