AFAIK the opf files are updated on edit/conversion so the should be up to date assuming you have backup to opf turned on. ( Wish I could turn it off
)
If you are worried about rebuilding, simply rename the metadata.db before rebuilding it or copy it to another location.
I had a corrupted database, which Chaley fixed for me. However after backing it up, I decided to reimport all 9000+ books (about 16 Gig) This took 3 hours which I thought was amazingly fast.
If it takes 2 or 3 hours, or even 10, it is not like you should have to do it every day.
I went through several panic attacks and I did lose about 50 books (not duplicates) somehow, but if and when I looked for them they were in the backup and easily recovered.
My current main library is 11422 books and I am sadly using a single core laptop from Romania (not a joke) and an old external hard drive. Calibre takes less than 20 seconds to load and be fully functional.
Helen