if the 4 wheel drive is gone in my 2001 Kia Sportage does this cause a vacuum leak

no this will not cause a vacuum leak

actaually depending on what you mean by " gone" i suppose it could as the front hubs are vacuum actuated. if the actuator is stuck open and trying to apply the vacuum it could be just venting it for lack of a better term. the actuator is on beside the drivers strut tower and has vacuum lines running to both front wheels.if the system no longer works i would cap off the actuator to make sure it doesnt cause you problems. but if the system is still there and just inoperative make sure the rubber lines to the front hubs havent split open causing the problem. this is by far in my experience the most common cause of 4wd failure in this model