What are your top tips to protect the site and the domain, should you find the worst happen?
I kind of mentioned these above but I'll spell 'em out.
My top tips would be:
* Local backups to restore to a different host because your backups at your host will probably be offline as well. Using a cloud backup service isn't a bad idea as long as they're in a different location using a different backbone. For instance you wouldn't want both to be on Peer 1's infrastructure.
* If you have multiple servers and your hosting company has multiple data center locations spread your servers around to various locations and keep your accounts mirrored so in an emergency at one data center you could switch the DNS on affected domains to the other servers. If feasible, spread your servers across multiple hosts but that's not always practical just from a configuration standpoint.
* Use 3rd party DNS on a different host and backbone. Where the DNS server is hosted actually your weakest link. If possible find a DNS service hosted in the side of a mountain protected by NORAD.
* Use alternative email accounts not in your primary domain for any required
* When possible, try to host with a company that uses redundant backbones.
Think about how it's linked together:
Registrar -> DNS server -> Hosting Company
I never put all 3 in the same location, ever. People that actually host with the registrar have a serious issue with all their eggs in one basket. Perfectly fine for sites you don't care about like the personal blog or family genealogy site but not fine for income sites that pay the bills.
If the registrar gets in trouble, which recently happened with hackers and DDOS targeting them, you may not be able to change your DNS servers if needed so at least be able to redirect your DNS elsewhere. Assuming the reason you're changing DNS is your host went down it's a good reason not to use your host for DNS. Being decoupled from the registrar and host can save your bacon in a crisis.
However, I assume if both your registrar and host are down, and they're in different geography and on different backbones, it's probably Armageddon anyway and perhaps planning for the end of the world is a little overkill ;)