Tried proving a negative once and gave up, arguing just wastes your breath.

Been there with the glue skin, and yeah, it can be saved sometimes. If the skin is just on top and the glue underneath still flows, I skim the film off with a palette knife, add a few drops of distilled water, and stir it slow for a bit. But once it has gone thick and stringy all the way through, I toss it, because you never get the right open time back and the bond gets weak. For the cracks you already got, I have had luck warming the spine folds with a hair dryer on low and pressing them again with a bone folder, though the marbled endpaper is probably a lost cause. Lesson I learned the hard way too: keep the pot sealed and check the hygrometer before you even mix.

Timing really depends on the store but most spots start marking down hot food an hour or two before close. My local one does it around 7:30 or 8 and if you wait past 8:30 theyre usually gone. Best bet is to just ask the deli worker next time what time they usually bag em up, they will usually tell you straight. Those bones are gold too, I do the same thing and freeze the carcass if im not making stock right away.