I can't speak to how likely it is D-V would go after these, but you can obviously infer from their UMG release schedule that things move much slower than with Sony, so they're probably a bit more discerning when it comes to choosing things - with Sony something like this would probably be an easy decision, but with UMG, do you want this at the expense of a pop twofer?
It's my understanding (via articles like
this LA Weekly piece from a few years back) that unlike some of UMG's other "problematic" (to say the least) storage facilities, the Capitol vaults are in good shape, temperature controlled and well cataloged and staffed by people who know what's there and how to take care of it. Given that those two Q8's were released as part of Capitol's short Q8 program of '74-'75 I would imagine that at the very least there are safety copies of the quad masters there, if not the original tapes.
There's another glimpse of the Capitol vaults in the video below, which was taken during a tour hosted by engineer Al Schmitt, who's done a whole bunch of 5.1 remixes including all of the Diana Krall albums, George Benson, Al Jarreau, etc.