A very good friend of mine took over a studio space that I used for years and on April 15th in '91 the big creek behind the building flooded.
When I was remodeling the building I had noticed a brown stain that ran around the inside walls.
We found out what it was when the water came up to the door knobs!
The flood destroyed all of the speakers in his 4 x 12" cabs, but he was able to salvage all of his guitars.
He had some nice stuff, too.
The water only come up high enough to reach the very bottom of his console, so he was OK there.
He was able to clean and dry out all of the rack gear that was under water.
He mostly had a big mess to clean up.
He lucked out because he got a government loan as part of a compensation package for victims of the flood.
My point is that he really didn't loose that much equipment once he dried everything out.
I think that he even had a decent studio drum kit that survived.
The scary part for me was that I had that space for over ten years prior to him leasing the building!
My JH24 would have been underwater.
Regarding the issue of power being on...
In this case the power to the building was still on when we waded across the street to check on the damage!
He went in the building, but I didn't because of the power being on.
If your equipment was not powered you'll be OK and it may not be a total loss even if it was powered.