What is the backstory behind why the company stopped selling this software? Has anyone asked the author or company about it? Would it be worth asking them to release the source since it's been so long since selling it?
Wollay and most software development he does is intermittent at best. The Cube World community went 6 years without an update. He will occasionally (every few years) post screenshots and teasers on social media, but it seems very clear that development of his projects is whimsical. I don't think anyone at this point would be surprised if he tweeted out tomorrow that he's done developing Cube World.
It also seems that Plasma was never actually sold. It was a preview that just required a free signup.
In the case of Cube World, he finally decided to come out of the wood and release the game on steam. Almost none of the feature he teased during those years were included in the release or were heavily changed, and even the core gameplay was very different than the beta, which made a lot of people angry.
He wrote an article explaining that the DDOS they suffered when first releasing Cube World had a lot of impact on his mental health and that is why he rarely communicated and then he disappeared again.
It also seems that Plasma was never actually sold. It was a preview that just required a free signup.