Amps are weird in that things can go wrong even whilst they’re not doing much.
All it would take is for just one component to fail...
It’s extremely rare, but not impossible.
However, in your case I don’t think there’s anything to worry about as the all important heat generating circuits were switched off. And even if they weren't, so what?
The general consensus seems to be that’s it better to leave your amp on rather than to keep powering it on and off.
Unless you’re talking heat generating Class A designs - or tubes.
With those you’d probably be better off powering them up for the listening duration only.
In any case, it’s just one of those things not worth worrying about when you want to immerse yourself in the music.
A bit like a meteorite hitting your house or Yellowstone Park erupting at an inopportune moment.
If it happens, it happens.
No point in worrying about such infinitely remote possibilities when your seeking pure sonic pleasure.