Haven't tried it yet, but potential feature idea – an option to try to find these dead bookmarks in archive.org & update the links instead of moving them to trash.
If you do this, which would be awesome actually and I second the request, I recommend shooting the bookmarks to http://web.archive.org/save/<url> to make sure the archive scrapes it at the time of bookmarking.
I like that! Could definitely see it being quite a valuable option, provided it was opt-in.