(2) A declaration for mental health treatment continues in effect for a period of three years or until revoked. The authority of a named attorney-in-fact and any alternative attorney-in-fact named in the declaration continues in effect as long as the declaration appointing the attorney-in-fact is in effect or until the attorney-in-fact has withdrawn. If a declaration for mental health treatment has been invoked and is in effect at the expiration of three years after its execution, the declaration remains effective until the principal is no longer incapable. [1993 c.442 §2]