The only way I could see a boresnake beaking off in a bore is if the wrong size is used. Like a .22 in a .177, .35 down a .308, and so on.
EVERY shooter, hunter I know owns at least one bore snake and the thousands of combined pass through all them bores have yet to cause a broken boresnake.
I have however seen cleaning rods break mid bore, and come unscrewed mid bore. Now I know you guys use a one piece rod, but the vast majority of people do not.
I am very careful when I clean my weapons, and have yet to have any method fail me. Both methods fail every now and then. Nothing is 100% but inspecting your equipment before and after use goes a long way to stop problems before they begin. I have more than one time had to delay cleaning because I had to go to the shop and get new cleaning parts because of parts I wouldn't put in my bore.