Spitfire, I see where you're going - trying to narrow the blame for the fatal accident on a swashplate that failed due to an overspeed. And maybe that did happen.
The Bell Maintenance Manual for the 206B does specify certain things that must be done when the main rotor goes above 114%. The gauge however only goes up to 120% so I doubt that anyone can say for sure what the value is once 120% is exceeded. And it doesn't really matter. Once you go above 114% you're "done." The mechanics get to take the machine apart.
But here's the deal: Above 114% the TT straps, fittings, pins and bolts all have to be scrapped. The blades must be inspected, and the damage tolerances are so strict (e.g. elongation of the bushing hole by .0015") that in any serious overspeed (like the one you describe) the blades would surely have to be replaced.
The manual then goes on to tell us about the tail rotor, and also the oil cooler both of which are susceptible to overspeed damage. But curiously it says nothing about the main transmission, swashplate or even tail rotor gearbox. (The engine is a different story and one must consult the appropriate engine manual for overspeed conditions/inspections.)
So the question becomes: Were these inspections properly complied with after the overspeed event?
You seem focused on the swashplate. The swashplate is "driven" by the drive link (that beefy hinged bracket that clamps to the bottom of the mast and connects to one side of the rotating swashplate). If the drive link were to fail then most certainly the aircraft would come apart. But, would the drive link become compromised in an overspeed? Bell does not seem too worried about it. Drive links *do* fail from time to time - perhaps this was the case. But there is no hourly inspection criteria nor life-limit for the link itself (at least, none that I could find in the 206 MM).
You mentioned that the pilot was very experienced. I know it sounds callous, but whenever I hear that, I think to myself, "So what?" Please do not think he was immune to pilot-error. High-time pilots crash too. I also have 10K+ hours, and I am just as capable of crashing a helicopter due to my own stupidity as the next guy. Nobody is immune from making mistakes.
The sad thing about helicopter crashes is that there is often too little wreckage left to make a definitive declaration of what caused the crash. It's even harder when you know the crew. So in this case, while the drive link/swashplate *could* have failed, it would be very hard to make that connection to the fatal accident without knowing exactly what was done to the ship after the first overspeed.