If you want to reclaim one of your authorizations from a machine you are no longer using, you can log into your account and go to Manage Devices. You will see a list of your activated devices, with a “Deactivate” button next to each one. You do not need to have access to a machine to deactivate it.
So if your computer is stolen or crashes, you can still reclaim its licenses on the Manage Devices page.