This is my nightmare. This is why I refuse to use 2FA. (Except on services that require it, and I wish they didn't require it.) Am I worried about getting hacked? Absolutely! But when I weigh the likelihood of (1) someone else getting into my account without 2FA and (2) locking myself out of my own account with 2FA, the latter seems much more likely! I understand how backup codes work. I promise you I will loose them…
I didn't lose a single account yet. I have printed backup codes, I have password manager, I have passwords backup in a text file on thumb drive, two copies. I have my domain held by registrar in my country, so I can just visit their office with my ID and talk with them. So I take some reasonable measures to protect myself. But I have no fear of losing those digital assets.
I actually gave a thought about protecting myself by creating a single 100% reliable email and then bind other accounts to that mail. Believe it or not: I didn't find any provider which would satisfy me. My worst case scenario: I'm going to jail for 20 years. Every free provider will delete my account after few years of inactivity. Paid providers usually are small enough so I wouldn't trust them anyway. My current plan is using my own domain with autopayment and enough balance on account. But of course that's not reliable. Registrar might just go bankrupt. And I can't really reserve my domain for 50 years no matter how much money would I pay.