VM recovery is almost done.
I lost my snapshots but didn't have too many of those so it's not worth the effort to try and get them back.
All of the important VMs seem to be fine (26 so far) and are back up and running. I haven't checked which snapshot the CI runner VMs are at yet but they're all booted and I can log into them so if I need to reconfigure the GPU driver or something to get working Vulkan that's not a big deal.
I haven't attempted to recover most of the Windows VMs yet. There's a lot of stale junk left over from earlier CI experiments so it might take a little while to figure out which image is which, but none of them are irreplaceable worst case.
Will definitely be adding the XAPI database to my backups in the future.
On the plus side the replacement DIMM is installed and happy so I have the full 512GB of RAM.