A: 50% of the time.
Sample size: 2
Source: personal experience
Guess my node will be down until Wednesday when I can get up there and bring it down to hopefully be flashed via USB.
But this is why I took a backup immediately before flashing it, and was flashing a node that I can get to without borrowing a bucket truck.
It's important to test these things in the lower risk environments first. The node on my workbench went just fine. The rooftop one disappeared.