How can you trust any company you pay to stay up even if you are their customer? I've used discontinued products before. Paid subscriptions to companies that merge with others and the service no longer really exists.
DNS resolvers aren't that expensive to run. Besides, one of the founders of dns0.eu has already scaled and sold a venture-backed startup (DailyMotion: https://archive.is/4pN5e), and currently employed as Director at Netflix. Pretty sure they can keep paying for dns0.eu servers for multiple decades. The only problem is maintenance, which is automatable to a large extent.