You wouldn't necessarily want to lose broken bookmarks. Metadata might be useful. They might be in an online archive. And you might be able to search for the link to find people who link to it for associated information.
Exactly, I use scripts to flag them up, and then manually appraise whether it's important enough to replace with an archive.org link, search to see if the data has shifted elsewhere (douglas self's site has gone through many such transformations in my bookmarks since the mid-90s) or just delete it.
True that. Just mark something as broken. Just in case, that website needs to have some metadata or notes even after it’s dead