I’ve updated Parallels twice without any issues with my existing VMs.
However ...
Just make a Finder copy of the virtual machine.
That’s what I was going to recommend.
If you (the OP) navigate in Finder to: Documents >> Parallels
You should see one or more PVM files (I have 8

), with names you should recognize from the Parallels startup/machine selection window. That’s your Windows VM, and it’s completely independent from your Parallels application. If you want to secure them, you can make a copy to a different directory, or even better to an external drive, and/or a cloud service like Dropbox.
On a separate note: if you’ve got business critical data not being backed up, you’re nuts.

Get an external hard drive _immediately_ connect it, setup Time Machine. On a Mac that has such a simple built-in backup, there’s no reason not to use it. Time Machine by default will include your VM directory.