I access my source code via the \\mac share, and that has saved my butt numerous times. I recommend not storing anything important on the VM--treat it as ephemeral data.
As long as the virtual hard disk isn't becoming corrupted, the data should be perfectly safe. I fail to see how the black screen would corrupt data, unless it happened mid automated save, but that would be very rare. You might need to elaborate on this a bit. It's not obvious how this relates to the issue.
Wouldn't we need to identify what the actual cause is for sure? I'm simply mitigating a potential side effect until Parallels can identify, and hopefully, resolve the issue. For now, its an unknown. Or are you suggesting that accessing the Mac Share is cause the back screen and moving my data back to the VM disk would resolve? If so, I would like to have expanded explanation on what is actually happening before I make that change.