Sounds like a sound policy to have.
I've only lost one link, wearenotcattle.com, it had this book, but archive.org has it now.
I was a little lost when that link went down.
The stss.nl link will come and go, too.
They are fighting the church's lawyers over copyrights.
They used to break the links after I'd share them, but it's been a year or more since the last time they weren't available.