212man: I had never pondered "mast bending," and am not sure if the bent mast in the 2013 accident is attributed to something that happened in the air, or happened about the time of ground impact.
(I have not read the NTSB report on that HEMS mishap, which would likely clear up my confusion).
But with that thought foremost: if the main rotor mast bent while at flight RPM, in powered flight, at some point between the top of the transmission case and the rotor hub, that would probably create some vibrations and loads that the attach points aren't built to withstand. I an not sure what would initiate such a bend.
(So this post is mostly speculation, sorry about that).