If the datastore contained critical VMs without backups, consider contacting or a professional data recovery service.
"All Paths Down" or "Permanent Device Loss" usually indicates a physical cabling or fabric issue.
VMFS (Virtual Machine File System) is VMware’s clustered file system. In ESXi 6.5, the primary version is (with limited support for VMFS-3). Common corruption causes include:
If your datastore appears in this list, it means ESXi sees the data but hasn't mounted it.