As others have said this article is poorly written with the person interviewed saying he was misquoted so nothing in it can be taken as true.

However, there have been very strong rumors for years that 2-3 episodes known to be in the hands of collectors (I believe it was said in a recorded interview with the Radio Free Skaro podcast by someone involved in Classic Who bluray releases)

While some people may be worried about legal implications I suspect that most just would rather keep it. If they really wanted to return it they could hand it off to someone who would be an intermediary. So the real danger is that once they die, whoever inherits their collection may not care about it and junk the whole thing.