It has happened to me a few times, needing to unclip on a hill. A few times the grade was too steep and too long, about a 20% grade that was over 1/2 mile, and I was down in my granny gear and it was too much. I looked for a paved drive on the side, turned into the drive because it was flat, and was able to unclip. A few times I didn't anticipate the grade being quite so steep, over 17%, didn't shift down in time, dropped the chain, couldn't unclip, and fell over. Falling over doesn't bother me. I get some road rash and rarely a bruise. I topple over a few times a year for whatever reason, usually a dropped chain and no time to unclip. I am not a dufus that drops my chain all of the time, but it does happen to me a few times a year.

For me the worse case scenario is being on a new rural route, go up a steep hill, and the steep grade ends at a stop sign on a busy rural highway with no flat area to unclip before reaching the highway. I learned to turn my bike to the right, pray there is a paved shoulder and then unclip.