What you need to distinguish is the vast differences in Software versus Books and other creative material.
It would be fairly easy to show that advances in graphics and other programming changes (Operating Systems) make software age far faster than books or other media does.
I would suggest the following:
After a period of 2 years with no sales of the software it reverts back to the original creator (company or individual) and if that is not possible it Becomes public domain.
This does not affect the rights of the Owner to any profits. The game/software may be published but on a not-for-profit status. In other words you may accept donations but not require them to play/use the software.
In our case the game would revert to Cryptic and if they did nothing with it for 12 months I would allow the software to be petitioned for release to public domain within 6 calendar months.
I don't see how that would be workable for number of reasons. First, not all software is individually and directly sold. For example, the Cryptic engine itself isn't sold. It would be tricky to determine when software was genuinely no longer in active publication, particularly for component software.
And imagine this hypothetical. I write software designed to manage very large businesses, but I only manage to convince one business to buy it. Two years later if I haven't found another customer does that mean everyone can now use it for free?
And here's a wild hypothetical. Suppose all the Oracle users groups worldwide staged a two year boycott of their software. In 730 days, they hit the jackpot and can use Oracle for free in perpetuity?
If you only require the software to be "for sale" whether it actually generates sales or not, that creates a different loophole. NCSoft could put CoH clients and servers up for sale for a billion dollars. They would then be for sale, but with no possibility of anyone actually buying them. Alternatively, NCSoft Korea could explicitly license CoH to NCI with strict orders not to load the servers anywhere. Technically speaking, the software is being actively licensed to a third party and thus "being sold" in the sense the law would likely have to recognize. How would the law distinguish between selling to another company and selling to individuals?