I like the point you are making in this post. It makes me think about the Backblaze blog posts where they discuss the likelihood of enough drive failures to lose user data. Then, they decided the calculation result hardly matters, because people are more likely to forget to pay due to an expired credit card or email spam filtering (missed renewal reminders!).
How do mega corps remember to pay their domain bills? Do they pay an (overpriced) registrar for "infinity" years of renewals? This seems like a genuinely hard business operations problem.
Mega corps have their own top-level domains. For example there're .apple, .google, .amazon, .youtube and probably some more I had forgotten.
Even when companies don't have their own top-level domain, they can have their own domain registrar. For example "facebook.com" is registered with "registrarsafe.com" as registrar. The latter registrar is a wholly owned subsidiary of Facebook. I learned this from this HN thread https://news.ycombinator.com/item?id=28751497
The megacorp that I work at requires us to surrender domain names payment that we own to a central authority who takes care of this in perpetuity. Any domain names we buy we also have to tell them about it. Your triple boss gets a good Stern talking to if you're not following these procedures.
Services like https://www.markmonitor.com/ sort this out. Notice that google.com is registered with them.
Not all registrars are super evil. Sometimes the domain just goes down and then your customers start barking and you have a chance to renew it.
Found this out when some of our emails started bouncing...