Is it possible to recover a device that was already deleted from my account?
No, and neither is possible to re-add a device that you don't have on your hands.
For Prey to properly work on a device, it needs to be installed and configured to your account. You could install Prey remotely on a mobile device by Google Play or AppStore, but you won't be able to configure the application to link the device to your account again.
Please, be very careful when deleting a device from your account. If you run short of device slots, our plans for Prey Pro have more capacity.