So you want to know how to save your characters,right?Well Im not using the GOG verison,so I may be wrong.Try to create a new/separate folder,then put all your character folders in it.You can put this new folder on your desktop until the reinstallation its done.Remeber to copy the SaveData folder,not each character separatley.Once its done reinstalling,drag the the folder back where it belongs.Either do this or copy the folder on a USB stick.