Sorry to hear about the crash. I too had a partial crash earlier this month, lost virtually all of my LPS, after 4 years of stability, and it was never explained. My theory is still that some temperature spike caused bleaching & killed zooxantellae, perhaps followed by some chain reactions.
Regarding your yellow leather, I once had one that would close like that every few weeks, remain closed for a few days, and then open up, better than before. Hopefully that may be the case with yours.
One thing I take home from this, it that this can happen to a large complete system such as yours, as well as to my small, sump-less 29 gal.
Good luck with the re-build.
Pete