> But what if a company does not excist anymore?
They may have sold it to another company or individual.
If not transferred, then the person who owned the company before it closed would still retain those rights personally.
It may be hard to find out who owns the rights, but that doesn't mean that no one does. If it's too much trouble to find out for certain, then it's best to not resell it, lest someone that you couldn't track down yourself have his lawyer come after you.
Think of i this way... Most of us thought a lot of old '80's games were abandoned and weren't going to go anywhere, so stealing them didn't lose anyone money because no one was selling it. Well, look around now, there's retro game packs, TV joystick games, and all kinds of stuff going on with many games that were said to be abandoned. Someone rounded up the rights holders, paid license fees, and is making money off that old stuff again. You don't know that any Amiga game rights holders aren't planning something similar, but even if not it still doesn't matter.
Anyone owning rights to something sold without their permission has the right to sue, even if the item in question isn't otherwise on the market at the time.
And look up what Disney and friends are trying to do to extend te copyright period. It's already longer than 10 years, and the big guys want it to be forever and ever, and are trying to inch along to get there.