Recommend paying 10 years in advance. Then at the 5-8 year mark, do it again.

What scenarios are you thinking about to lose the domain? To me, the most common would be forget the pay the bill, or your credit card on file expires.

A light Google search tells me that it is possible with several different providers to pay for up to 10 years in advance. Still, the exact same issues can happen at the 10 years and 1 day mark! How do large corporations handle this problem? Do they have a special contract where the domain register will always keep the domain registered, then bill the corporation directly? That seems like a business venture with juicy margins.

The most common answer is to hire MarkMonitor to do this for you.

I have the opposite problem. I want to get rid of email at a legacy unattractive domain but it's still appearing here and there so I keep paying for it and preserve the setup for it.

And that's the real hard part

Have you ever lost a domain? I haven’t despite having many domains across a number of registrars over the years. Are people just using bad registrars or what?

Yes, I have. Due to a human mistake we lost a family domain, where I hosted one of my important e-mails.

Sorry to hear that. Some registrars let you pre pay for multiple years now, it’s a good idea if you have a crucial domain that you know you will be holding onto.

Did you try to contact ICANN and explain the issue? If you could prove ownership for many years, your case would be quite strong.