Simple as that.

I guess no user will be happy for saving extra 100 kB of disk for the cost of loosing extra 5 hours of work ;)

Make Autosave Feature ON by default!

And if you can - make it also save w few files, and prevent it from overwriting (without a warning!) itself when having two or three instances open. Every instance could have a random session ID and save the autosave files with this session-ID prefix like:

 57567-recovery-01.mmpz
 57567-recovery-02.mmpz
 57567-recovery-03.mmpz
 96817-recovery-01.mmpz
 57567-recovery-02.mmpz
 12422-recovery-01.mmpz
 29500-recovery-01.mmpz

Also a dedicated folder for autosave files could be nice, and a button for opening file browser in that directory would be great too.