No, you can't. Your instance will go down, but all your posts and comments will still live in read-only mode on the instances they been federated before.
In mastodon (another activity pub service) you can export your account with subscriptions, but not the posts. So, if it'll happen, you gotta start from scratch.
Maybe Photoprism isn't a backup strategy, but Syncthing for sure is, because you can have multiple backup units in it.
I'm additionally use software RAID on one of devices, that receives Syncthing backups.