Imagine if copyright at works went into the public domain after 25 years. So many books, albums, and games are in this bizarre limbo where the rights holders may no longer exist, but they can't be freely distributed due to copyright laws. Or even if the rights holder does exist, they might have no interest in releasing the material due to current creative differences ( or licensing, tons of video games based around other intellectual property will never be released again).
I would say that if something doesn't get published when there is a guaranteed, government-backed monopoly in place, then it's even less likely to get published when there isn't.
I don't think it's common for stuff to go unpublished when no one can find the copyright holder. In that case, just publish it and wait to see who complains.
Show me one person who actually thinks that.