I had undergone maxillo-facial surgery a month ago. How long until the swelling and numbness go away?

Up to 1 year . The majority of the swelling should resolve within 6 to 8 weeks. The remainder of the swelling (although very small amount ) will resolve over several months. Depending upon what type of surgery was performed numbness will resolve anywhere from 3 months to 1 year. Nerves repair themselves much slower than bones or skin. Hang in there the toughest time is behind you.