I agree that this specimen looks from the outside like a typical Disholcaspis quercusglobulus gall, so I wonder if the inside scene might just be an atypical situation in which the gall-maker did not mature and escape in a normal schedule. To test this idea, I retrieved a photo I had taken of an adjacent gall on the same fallen branch and checked it for an exit hole - which it did have (see fourth photo, just added).

The BG Info Tab relates that "galls in Ohio have been observed to contain pupae in late September; adults emerged from galls in Ohio and Toronto in mid- to late October." Perhaps mine is one that failed to emerge last fall and whose cadaver was preserved from dessication and decomposition during the winter by cool temperatures and protection within the dense gall tissue, then discovered by me in March. If so, I erred is describing it as "live", it merely appeared life-like due to its intact condition. Also, I used the term "larva", but perhaps it is actually a pupa?

whether that was a larva or a pupa. Check out the discussion under this image

of galls that still had larvae in December... there is clearly much still to be learned about these common galls.