Activation Lock for Mac - Apple Support
For information relating to 'How to delete your Apple ID account', click here --> https://support.apple.com/HT208504
"Make sure that you sign out of all your devices to avoid issues with apps that use your Apple ID account or iCloud. After your account is deleted, you can't sign out of iCloud or turn off Find My iPhone Activation Lock on your devices. If you forget to sign out, you might not be able to use your device when your account is deleted."
Apple can reset a device if a person can provide sufficient evidence of valid ownership. Try this online here --> https://al-support.apple.com/#/additional-support (Yes, apparently this does work in this situation too: https://discussions.apple.com/thread/253344078?answerId=256255850022#256255850022 )