Snapshots are often a big problem in many environments, people always forget they are running and many people are confused on how they work. If you are running 8 VM’s on a single server I’m going to assume that you are most likely using ESX. First thing I would check is that your virtual disks are not set to Independent, Nonpersistent, you can check this by editing the VM’s settings and selecting the virtual disk. Nonpersistent disks will discard all changes when the virtual machine is powered off.
Rebooting a host will not cause it to automatically revert to a snapshot. It is possible they you ran out of disk on your ESX server which caused issues with them. As far as recovering data it’s probably unlikely but depends on the situation. If there was only a single snapshot on the VM and it reverted back then the current state is wiped out once it reverts. If the VM had multiple snapshots it is possible to go to a later snapshot if he reverted back to an earlier one, however current state is again wiped out when you revert.
If you have a VM with more then one disk and you wish to exclude a disk from being included in a snapshot, you must edit the VM’s settings by changing the disk mode to Independent (make sure you select Persistent). The independent setting provides you the means to control how each disk functions independently, there is no difference to the disk file or structure. Once a disk is Independent it will not be included in any snapshots.
I did a 3-part series on snapshots a few months ago on searchvmware.com that covers everything you need to know about them.