Just as a data point, a few years ago I cut into a foam flying boat hull I'd built in the early 70's. Sourghum was used to attach 1/16" balsa that was then glassed. It had been flown a number of times before being set aside.

What I found was that even after all those years the skins were so tightly bonded that I couldn't get them off without ripping the foam apart.

However, I know from the experience of two friends who had the same flying boats without glassing them (one used Monokote and the other stored his unfinished in an unheated detached garage) that Sourghum will eventually lose its grip in the presence of moisture.

None of this is meant to suggest the bond on the Aurora wing didn't fail. The Sourgum may not have been applied properly, it may have been exposed to dampness at some time or something else. All I can gather from my experience is that it doesn't loose its grip with age alone.

FWIW