My dad is 70. He just had aortic valve replacement. Does he need a permenant pacemaker?

Need for pacer? Assuming your father had aortic stenosis, the need for a valve replacement is totally separate from any need for a pacemaker. A pacemaker's function is usually to allow a control of the heart rhythm in the case of the heart's normal rhythm being abnormal or undependable. Most rhythm problems respond to oral medication but some require a pacemaker. Valve disease is usually a separate issue.
No. Not unless he has a rhythm or rate problem which is not medication related. If he remains in sinus rhythm and has a good rate, no other therapy is needed. Pacemakers are reserved for rate issues (usually slow rates), or rhythm problems.
No. Less than 5% of patients who have avr require a permanent pace maker post op.