I worked for a company that sold third level domains. The company got bought out a few times as it kept going bust and the market consolidated, but unfortunately, the final owners did not understand what they had - I’d long left by that point - and they let the root domain lapse.

Perhaps as a saving grace, no-one had been maintaining the infrastructure (I was one of the last), and it ceased to function at a technical level long before the domain ended up lapsing. That gave people an unpleasant kick up the rear end to move their important stuff elsewhere if they hadn’t already. (The price we sold it at compared to actual domains ought to have been a hint that it wasn’t for important stuff, to be fair.)

I heard talk of a potential lawsuit against the ultimate asset holders, but I don’t think anything came of it.

Theoretically, the current owners of the domain could do what this guy talks about in order to try to collect mail for those accounts, but they’d have to know which subdomains to set up in order to do that.

I had one of those domains, and yes I got my stuff onto a proper domain not long after I left.

I also had a couple of accounts with a non-Google free e-mail provider that went under. Unrelated to my employer. The domain ended up belonging to an individual who probably gets a heck of a lot of email for former users of that service.