Twice properly-adjusted rear derailleurs have gotten into the spokes of my rear wheel. That's in 40 years of riding bicycles with gears, so it isn't often. The first time happened when I was riding on a dirt road with a lot of loose stuff and picked up a branch, the second time when I took my bicycle out of a hitching post - apparently a neighbor had hit the derailleur, bending it into the spokes. I've bent the hanger, broken spokes, destroyed derailleurs. I have bought replacements at Niagara Cycle and e Bike Stop