NOTE: It's probably not worth reading too much into the outward comprehension of how good-or-not StackExchange is at managing their disaster recovery scenarios. I suspect they are following much of the best practice below and simply testing scenarios to validate their configuration.
Depending on the environment you operate within:
A disaster recovery plan ...
You can use helm get manifest <RELEASE_NAME> to fetch the kubernets manifests and you can use helm get values <RELEASE_NAME> to get the values.yaml from the cluster. But I don't think there is any way to get the chart files back. Sorry.
PS: Please replace <RELEASE_NAME> with your release name.
You don't mention orchestration, are you planning to implement all by your own configuration on top of Ubuntu?
I recommend you that take a look at Kubernetes and StatefulSet workloads
You can use Ubuntu as your host to accomplish your needs, but in my experience, you can only need to ...
In terms of S3, for increased durability, consider cross region replication as an option if you want to increase the durability. AWS also provides their AWS Backup service you might investigate. I'm not certain of any benefit to transferring large amounts of data for durability to another provider. You'll pay a lot more for transfer, and it won't be ...