I've had domains registered for over 20 years already, much longer than gmail has existed. You can renew a domain for ten years in advance and easily transfer

I've had domains registered for over 20 years already, much longer than gmail has existed. You can renew a domain for ten years in advance and easily transfer between registrars (and email providers, I use Fastmail), so it's a lot more reliable for the (very) long term than a third-party service.