and the best way to do that is to reboot the machine.

Not sure why you think that all your work will be missing when the machine reboots though. Presumably you were saving each, and every, scan as you produced them and again after you rotated them.

However, if this is not the case, then yes, all your work will have been for naught.

The Finder, like Windows Explorer, is a very important part of the Operating System which will not work correctly if the Finder is not running.

Reboot is your only option