One for the engineers amongst the assembled masses.
Exactly how quickly would the AI and DI start to wind down to give spurious information? Also, as the vacuum pump is linked to the engine, and your prop is windmilling then would this still be driving the pump? and would there enough suction to provide a 'useful' AI and DI.
Just wondering because the initial reaction to anything this serious would be to believe your instruments, which could present even more problems when you do break cloud inverted! Vne or not, not much time to get sunny side up.
Tis a silly thing to do anyway.....