One of the first things I did after the house fire was run upstairs to see if my totes full of Celtic/megaliths/ancient UK history books had survived.
Some got a bit wet but were salvageable and I was so relieved.
I have books out of print I could never replace.
The bog body books were okay.
Like you, I also have long out of print books, that would be impossible to replace and IF I lost, would break my heart.