Virtual desktops are not produced by KDE but by the underlying X windowing system. You can have them in Gnome or LXDE or whatever you want to use.
There was no harm in using a VM to handle e-mail, but you should have arranged for the mail to be backed up regularly because any computer can lose data at any time. You will now have to do whatever you can to try to recover the file(s) containing your e-mails from the virtual disc files. The first thing you should do is make a copy of those files somewhere other than your current computer and work only on that copy. If you mess it up you can make another copy to work on.
I quite understand the problems with KDE which forced many of us away from kmail and kontact. I went to Thunderbird and others went to other E-mail clients and contact suites. There are plenty of them in Linux, but if you found Outlook in a VM best suited your needs that was fine - so long as you backed up its files as with any business-critical data.
There is also no harm in using snapshots to provide an easy return path if a modification causes problems, but there was no need to keep the snapshots once the return was no longer necessary or desirable. Snapshots slow down the VM and introduce complexity. 20 layers of snapshot is asking for trouble. It's just multiplying the number of things that can go wrong. Now you can return to a snapshot you find it's no good to you, in which case there's no point having it.
There are plenty of people on this forum who know about disc recovery software and there are quite a few posts with information that might point you in the right direction. I just hope the data isn't so scrambled by switching off the recovery program that something can still be found.
And yes, safe mode might be worth a try, but copy everything first so the original is safe. You cannot risk further damage.