I bought a G-103 that had been in a hangar fire in Georgia, Peach State Club. We needed a left wing and the photos showed what looked like a useable left wing on a fuselage with canopies that had been hot enough to melt the canopies. Both canopied draped down like a tarp, but it was the new shape of the plexiglass! The outer skin of the left wing top was blistered and had to be replaced, but the spar caps were undamaged. I figured the wing hadn’t been in 350 degree environment long enough to affect the more dense spar cap. We proof-loaded the wing and it took 5.3 G’s with flying colors! That was some 25 years ago and that ship is still flying today!
Just a little data point about how much heat a fiberglass structure can take,
JJ