Today minivmac crashed when I tried to run HyperCard. After restarting the emulator the virtual hard-disc with all my Mac software on it was not recognized any longer by minivmac. It said "no Macintosh disc. Do you want to initialize it". I tried to use the file with HFV-Explorer, but that wouldn't work either. Any way to recover my data from that virtual hard disc or is it all gone now?
Btw, I am using minivmac on Win XP, so the solution via OS-X-DiskImageMounter won't work out for me.
The readme file says that default disk images can be recovered in OSX mounting once with Disk Utility. Whether this works with .hfv files is debatable.
Best of luck! (I know how you feel, I lost a 270MB HFV file myself) 
Restore from backup.
Happens to all of us once, even on Mac OS X. After the first time, you learn to back it up - once a week for me.
I have had my (already old) Mac CDs stored away for more than 7 years. When I pulled them out recently, some of them had CLEAR sections, as in 'pane of glass' clear. There are now 2 whole CDs I cannot use (I did back up what I could from one, before it failed completely). Many many disc read errors on some of the others.
It would probably be a good idea to backup everything Mac as .hqx, and store on a perfectly stored DVD - copying the DVD(
every 5 years or so. That is what would happen in a perfect world...
