We need TVOC...
...to go tits up, I think. That will force the HLF's hand viz-a-viz an investigation, and fix the immediate management problem at the same time, at a stroke. The aircraft will not evaporate in a puff of smoke if TVOC goes bust, and nor will the engineers or the people with the knowledge.
Giving TVOC money to continue to pee up the hangar wall in secret and nothing changes except donors get poorer and confidence in the project ebbs further.
I reckon the optimal way forward (as somebody not privvy to what is or has really been going on and fed up that his donations may well have been wasted) is to cut them off, donate not a bean, wait until the gravy train shudders to a halt and they are forced to account for themselves to the HLF and then hope that the Vulcan rises pheonix like from the ashes.