My pants get sucked into my chain all the time, and I've shredded many old right pant-legs that way (yes, I know I should really do something about that...) Yet, I've never actually had this pose any kind of threat to me. The cloth gets caught in the chain, goes around the chainring, and comes out the bottom. Nothing at all like these stories of people's legs getting sucked into the chainring until they fall off the bike. I can only imagine that the main reason people crash from this is not that they were actually pulled off, but that they freaked out when they saw their pant was caught and this freaking out (including any possible misguided attempts at pulling the pant out of the chain) results in the loss of control.