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#21
In Windows 7 to 8 upgrades the Windows.old directory was automatically deleted after 4 weeks by cleanmgr.exe
Windows 8 drivers, Windows.Old files |
Missing Windows.old folder after upgrade
If this is the same in Windows 10 (and no-one knows) then your automatic ability to revert would be lost as the windows.old directory wouldn't exist anymore on your C: drive. This is nothing to do with licenses and nothing to do with OEM software - it is only the Windows.old directory is deleted by the OS after a month (in windows 8).
Best to make a backup IMO. Just before and just after upgrading would be best if you have space.