(1) The DMCA, and for that matter copyright law generally, creates private rights of action in the copyright owner. Even if something is infringing on their rights they need not act. The decision is up to them.
(2) Copyrights do not pass automatically. Nobody can pick up the torch by asserting the rights of an inactive copyright owner.
(3) True abandonware involves either a disappeared copyright owner or one that no longer cares about an old title.
So ... do what you want with abandonware. If the copyright owner reappears and asserts his/her rights, then it wasn't really abandonware in the first place. That's the risk you run.
Also, copyright isn't what stops people from maintaining old games. It might be the easiest means of enforcement (ie takedown notices) but it isn't the meat. Nobody cares if you make copies of the original Civilization. The copyrighted game is valueless. But they do really really care about you using the "Civilization" trademark. That tidbit of intellectual property has nothing to do with the DMCA.