nice setup. 
while using an email aliasing service I suppose? Portability is quite more simple in that situation yes. 
If you keep a local database only and no account on their servers, why not Keepass then? I mean, is it even feasible to have a Bitwarden without an account on their servers?
I’m not familiar with this one specifically but I do prefer a good old physical hardware key (ex: Yubikey) for a safer approach. Hopefully you can still access the 2FA authenticator if you lose access to your Bitwarden vault.
Storing physical backups at family/friends/other safe place is indeed the way to go.
Consider doing digital backups of things too, on a cloud somewhere encrypted.
This locks you down to Apple’s ecosystem tho. 
Consider having physical backups + trusted family member or alike. 
Some registrars allow to buy a domain name for 10 years ahead of time.
And they send plenty of reminders before expiry.
And you can also create a specific bank account that has always just enough money for those yearly checks to go through.
Also maybe a calendar reminder?
Overall, plenty of solutions don’t worry too much. 
And even if you get through all of that, it doesn’t mean that somebody will steal it straight away: you can always buy it back from the registrar for a slight fee.
Owning a domain is not as scary as it sounds. 
Not sure how it is related here.
Maybe give a read to this one then?