Here is what happens if you unplug external 10GB IDE HDD

see attachment

 

There is still local past edit history (Tools|Options|Misc|Versioning|Local History to set how many days to store) but what can a program do if it's editor storage drive is gone?

 

It is also closing down the edit window,
and greying it out in the project view.

When I plug back the USB drive, it needs "refresh"
in the project window.

 

What do you expect the program to if the open file descriptors are closed by the drive going away?
It might be able to recover if it's plugged back in but don't unplug the USB drive while editing and always have backups on different media.

 

The regular MPLAB isn't as precize about that I think.

And yes it becomes available again when I plug back in the HDD.

I never used removeable HDD until recently.
Yes don't unplug while it is accessed, normally only when the application using the file also has been closed already.