You can import a datastore in any PBS and all your snapshots and backups will be available. As long as those drives are safe, you don't really need anything else to access your bakups.
If you want to backup PBS settings (task scheduling, etc), just save a copy of
/etc/proxmox-backup
(or the whole
/etc
), reinstall, and copy the relevant files back. Of course, it doesn't hurt to have some "clonezilla" of the drive where the OS is installed, but it isn't really a must.
Anyway, having a second PBS or at least a USB drive as another datastore and do syncs there is preferred over any single PBS