It sounds like they had a really bad backup system for this to happen.
No one will ever trust them with their data and email again, so they might as well close their doors straight away. It’s unfortunate but a mistake like this is likely gonna cost you your business.
It's not offsite backups that would have saved them, it's offline backups.
You can have all the data centers you want, but if they're all connected, then one ransomware attack can (and did) nuke them all.
If you have just one system that's unplugged with a copy of all the data, then your data will be fine. It's just time at that point, which could still be very very bad, but the data still exists.
Or something like AWS S3 vault lock. You pay up front and specify the duration. And at that point you can't even delete the data if you want to. You can remove you're credit card from account billing, and they still keep the data for the specified duration.
Pretty sure the Amazon vault lock offerings are essentially specific implementations of the broad idea of an immutable backup. Not disagreeing with you here, just saying this might not be an “or” situation.
Off-site can also be offline. Any serious company has a tape library stored in another location in a vault for worst case scenarios. Since fire and natural disasters are also a serious risk.
Sure, but those are two different things. Offsite is good to protect against natural disasters (or attacks, or...), offline is good to protect against digital disasters (ransomware, admin mistakes, etc.)
Tape libraries are a way to store offline backups, but they don't have to be offline and aren't the only way to run a backup solution. They are a way to store data in bulk for cheap. They are also a way to help protect against technological changes (if all your backups are on 5 1/4" floppy discs and you can't find any 5 1/4" floppy drives, then your backups are no good).
Some people like to use a 3-2-1 solution (3 copies, 2 different technologies, 1 offsite), but that doesn't specifically mention anything about offline, which is critical for these types of situations, and the exact solution has many different correct answers.