Phew - wotta mess !
Hey, at least on an R22 it could just fly out the back - The R44 is more enclosed and it looks as though that's helped this one to do a whole load of damage !
There's a big nut with a retaining pin though it that holds the fan to the shaft. The pin is supposed to line up with witness marks on the fan itself. I always check this on my walkround. One time I noticed that the pin wasn't lined up with the marks - and decided not to fly until it had been checked. Glad I did now !!!
Be interesting to find out in due course what the cause of this one was - it looks well shredded.