What is the average "zombie" subscription rate for per 1k subscription?

I currently have 54 subscribers for my RPG, but almost 90% of players cancel their subscription after just 2–3 weeks. Since it’s an RPG, once they reach the high levels and get their "dopamine hit," they feel they’ve finished the content and unsubscribe.

I’m considering switching from an $8.90 monthly subscription to a $19.90 one-time purchase. Before I do, I’m curious about "zombie" subscription rates. If I had 1,000 subscribers, how many people typically forget to cancel? If 20–30 people stay subscribed without playing, that’s $200–$300 of passive income.

Is it better to stick with the subscription model and hope for "zombie" revenue, or should I just take the higher upfront payment? What do you think?