Got the data, perhaps someone would find it useful.
$vmName = "Test VM"
$vm = Get-VM $vmname
$vmGlobal = Get-WMIObject -class Msvm_VirtualSystemGlobalSettingData -namespace "root/virtualization" | where {$_.systemname -eq $vm.name}
$vmRootPath = $vmGlobal.ExternalDataRoot
$snapshotPath = $vmGlobal.SnapshotDataRoot
Then, get these paths, append "Snapshots" to snapshot path (apparently hardcoded), append "Virtual Machines" to root path, and get configuration and snapshot files. Disks could be received by calling $vm | Get-VMDisk | where {$_.DiskName -eq "Hard Disk Image"}
, these contain absolute paths to the files.
This should be enough for me to get all data required to back up and restore a VM from a snapshot, even in case the original VM is destroyed due to disk loss. I'd probably have to mess up with the backed up XML to change paths, but this is a bit easier.