I really hope Nutaku reconsider this, but if they want to go full-greedy on their decisions, then we can use one of the free-market's basic concept to let them know this is a really bad choice.

Stop rewarding them with our preference! The demand for their services is what sustains their social media campaign, marketing campaigns, etc. which in turn enables them to reach more people and potential paying customers.

If they actually shut down the game, it is clear for me that I have to unsub, unfollow, etc any of their media stuff, as well as obviously not to visit the platform itself, let alone make any purchase.
As insignificant as it sounds, but given MWA's player base, these simple actions as a group will impact them.

Also, for those who paid recently, you can always dispute the purchases made on it, and use the service closure notification as proof of the service not being provided as satisfactory as offered. But that's a last resort that could backfire. Let's wait and hope Nutaku rethinks this.