What exactly do you have in mind?
Every version of the state file associated with you stack is stored in your backend - pulumi.com by default, but you can use local disk of cloud storage instead.
07/15/2019, 7:29 PM
We are wondering if pulumi backs up pulumi-hosted stacks.
07/15/2019, 7:41 PM
Yes - all state files for stacks managed by the pulumi.com backend are stored in durable cloud storage (currently S3 - which claims 99.999999999% durability) and cross-region replicated for increased availability in case of catastrophic regional outage.