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If an authoritative DNS entry was removed, it can take up to 72 hours for that change to be propagated around the world, though usually just a few hours for some other authoritative DNS systems to get you mostly back:

https://ns1.com/resources/dns-propagation#:~:text=DNS%20prop....

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Why it takes this long?

Caching

Resolvers typically cache successful "does not exist" responses for no more than 1-3 hours. (And authoritative servers often have a lower negative TTL.)

(There's a corner case related to DNSSEC that can make it go higher, but that's being worked on, and isn't relevant here.)

In this situation, the nameservers were just down. I haven't done exhaustive research, but the resolvers I'm aware of cache that kind of thing for no more than 15 minutes.

If there’s a chain of caches 3 deep, a 15 minute cache on bad responses will take 45 minutes to clear.

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