Is my license key still valid after I reinstall my OS?
Yes, you can reactivate on the new device without limitation whether it's because you lost your devices or reinstall the OS. Each set of the license can be activated on two devices and run on both Windows and macOS, you can switch devices you want to be activated however you want.
Remark: When the license key is activated on more than 3 devices , Eagle will provide you a management interface to manage your device. You can still use Eagle without limitation.