Idk about that, the people who supported did so under the context that the dev was eventually going to release a completed game.
This goes mostly for the Ci-En supporters (since the Part 2 of the game would've been a separate final product, much like with the MGQ series), and really here it's a more complex issue between the supporters and the creator.
In theory, when you support somebody on Patreon/Ci-en etc. (platforms with recurring monthly payments in the form of subscriptions), you support a specific action that said creator's currently ongoing (such as Artist making art, mangaka's writing stories, gamedevs developing games etc.). However, you can stop such support at the moment you judge you do not support what's currently ongoing, or when you judge that said thing is not currently ongoing anymore (eg: games being abandoned).
So basically, it's fine if you unsub from this creator from Ci-En now that you know he's likely not going to produce game content anymore (if you were subbed to him to support that endeavor of his). However, your money spent up until then were spent appropriately, since up until that moment, he had been developing his games (and successfully publishing 2 so far), so you can't actually ask for refunds since you did enjoy the monthly content he produced up until then.
And on the topic of "asking for refunds", you certainly cannot simply demand a developer open-source or distribute his game for free simply on the basis that he will not be further continuing the story of said game. He still developed a product at the end of the day, set a price to it, and people have bought it for its current content (for the expectation of future content, you generally can further support him on Ci-En).
Really he doesn't owe anybody him losing a well-earned stream of revenue (I mean the selling of the game; his Ci-En should be suspended by himself if he stops making content imo). What would be nice of him, instead, is him being willing and open to the idea of another future gamedev taking over the project and continuing the game, making a part 2 for it (from which he could negotiate a cut of the profits for the "IP rights" themselves; and thus both parties enjoy their profits, while the public enjoy further content in this "IP").