This is not the case for copyright, at least in the US. You do lose patent, trademark, and trade secret, for failing to defend, but not copyright. One loses the right to collect damages against parties who infringe too long, but not new parties. (Except if there’s a case that could rise to the level of creating a latches defense, but that’s different than losing the right, and is pretty unique).

That said, CSW is fraudulently claiming copyright, so it’s a moot point with regard to him.