Go to bed. Don’t stress. Your banana bread will be fine on the counter for one night.
In the morning, grab a slice, pour coffee, and enjoy the victory. You planned ahead for breakfast.
If anyone questions you, tell them a food scientist said it’s okay. (I’m not a food scientist, but I play one in my kitchen.)
The only real danger is that you’ll eat the whole loaf by lunch. That’s a risk I’m willing to take.
So, yes, banana bread can sit out overnight. Now go eat a slice. You earned it.