Root servers only control the mapping up to the TLD. That is, they for instance know the nameservers for ".br", but they know nothing about the nameservers for ".com.br", or about the domains below that. If your domain is "example.com.br", the nameservers which could "just take it down" are the nameservers for ".com.br", not the root nameservers. In the same way, the root servers are completely unrelated to domain registrations (other than pointing to nameservers which know about them).
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What if root servers just take it down? Retract the domain registration, etc.
Root servers only control the mapping up to the TLD. That is, they for instance know the nameservers for ".br", but they know nothing about the nameservers for ".com.br", or about the domains below that. If your domain is "example.com.br", the nameservers which could "just take it down" are the nameservers for ".com.br", not the root nameservers. In the same way, the root servers are completely unrelated to domain registrations (other than pointing to nameservers which know about them).
Then noone could resolve it, including Quad9, CloudFlare, Cisco, Google etc.
Your resolver can resolve any domain to any IP.
As long as it’s a static IP and the server is still there, you’d still have access as long as you had that mapping.