For all the many years I've used VMware Fusion, I've kept my VM folder at the root of my internal drive. This works for me, I'm the sole user of the machine.
The install/upgrade of High Sierra just evaporated that folder and its contents on two different MacBook Pros. Thankfully, I always do a couple of TimeMachine backups before any upgrade like that and could readily restore them but beware of this nasty behavior of the MacOS installer. I think this happened once before on an OSx upgrade a few years back also. I'm guessing it's the versions that change the file system; in this case it became APFS on the SSD.
BTW, on another computer, a separate small folder of screensaver art files that sat in the root was left untouched. Why did /vm go but /art was left intact?