If a company goes bankrupt, the copyright passes to *somebody*. The work does *not* automatically go into the public domain any quicker than it would if the company was still operating.

As works are protected for 50 to 100 years (depending on circumstances) and personal computers haven't been around that long, there is *no* software in the public domain that hasn't been *deliberately* placed there by the copyright holder(s).

Some companies have made their older games available as freeware, but they are under no obligation to do so.