It won't cut it off, but it'll hurt like hell, and bruise quite nicely. This I know from experience . FP helis don't have a high enough headspeed to do any 'real' damage. If you go to collective pitch helicopters in the same size range, i'd suppose they'd probably have enough physical enertia to break finger bones on contact. Should a blade happen to come off during flight on a collective pitch helicopter, well, it's a good chance they'd have enough enertia to impale you if you got in the way and it hit you straight on. Obviously, the odds of that happening are like 1 in a million but the power is still there, and so is the threat, so it's always good to do proper pre-flight checks every time you fly .

The danger vs death ratio goes up considerably the bigger the helicopter gets, especially if they're using fibreglass blades. It won't be the first time someone has died from an RC helicopter. I think there was a topic on this just recently, probably a few pages back, if it interests you.