For starters, it ain't retreating blade stall.
You referred to mast bending - this is part of the overall stresses on the aircraft - the disc tilts forward to drag the fuselage through the air, and the horizontal stabiliser tries to pull the tail down to keep the cabin level and comfortable for the pax. In the middle is the transmission, its mounts, and the mast, which have to absorb these bending stresses.
The advancing blade tip speed starts to reach the mach drag rise, stressing the blade and making the Xmsn work harder for every advancing blade.
You will also start to run out of cyclic movement, or reach the place where cyclic displacement goes the wrong way, so it is unable to ensure stability as per the definitions.
Yes you can exceed Vne, but you are entering the area where things can be a little unpredictable, and the wear and tear will increase dramatically. I have been in an S76 (Vne 155kt) that hit 180kt when crossing a windshear, 35kt tailwind into a 40kt headwind. Massive balloon upwards despite dumping the collective.