If I transfer authorizations from the current keypad to keypad 2.0, what happens to the old one. Can it be reset afterwards and given to someone else?
It is not reset automatically, but the authorization in deleted on the Smart Lock side. i.e. the Keypad can not communicate with the Smart Lock anymore.
If you want to give it to someone else you have to either pass along the Admin PIN too or factory reset it through the Nuki App > Menu > Help > Factory reset.