That is the worse with Youtube, not that you don't have access to the video anymore but that you don't even have the title anymore so if you don't have a good memory, you have no clue of what piece of knowledge you lost from your library.
That's the thing though, it was never yours. Just a corner in Google's library that they let you curate. You don't have to do that. It was never a good deal.
Then, usually you play the list by itself from random position and order. So I quite often listen to them, but for a playlist of maybe 50 entries, i will just noticed that things disappeared when looking at the "hidden entries" thing.