The office of state senator or representative shall become vacant on the happening of any of the following events, before the expiration of the term of such office: The death of the incumbent; his resignation; his removal from office; his ceasing to be an inhabitant of the district for which he shall have been elected; the decision of a competent tribunal declaring void his election or appointment; or his refusal or neglect to take and subscribe to his oath of office. Regardless of any change in the boundaries of any state senatorial or representative district, an incumbent state senator or representative shall continue to represent the district from which he was elected until his current term of office shall expire or his successor is elected and qualified.