For several decades, old fighters have been rigged with remote control capability, so they can be flown without pilots. This way, the old aircraft can be used as targets for air-to-air, or ground-to-air missiles. As far back as the 1970s, such robotic fighters were even successfully used in tests of air-to-air combat operations. All this experience has been used in developing a new generation of robotic combat aircraft. Actually, the first generation of such aircraft will be remotely controlled from the ground, or another aircraft, most of the time. This is possible now because of improvements in communications (especially via satellite links) and sensors (cameras and radars) to give the remote pilots a better sense of where they are. This "situational awareness" is essential for air combat. It is not as essential for delivering the current generation of smart bombs (especially the GPS guided bombs.) Thus UAVs are already being used for bombing missions.
But new advances in flight control software, and sensors (more of them, cheaper and with better capabilities), make it possible to build robotic fighters, and bombers that can operate by themselves. Such capabilities already exist, as current flight control software will act to protect the aircraft if communications is lost with the human controller. Actually, robotic bombers have been around for half a century, they're called cruise missiles. Before the Tomahawk was developed, the navy had several pilotless aircraft designed to deliver nuclear weapons all by themselves. But the new generation of robotic (as opposed to remotely controlled) bombers will receive their orders, and then be sent off to do the job (with a human flight commander observing it all remotely, ready to abort anything not going according to plan.
The in-flight refueling is necessary because unmanned, as well as manned, aircraft can carry more weapons if they can refuel during the mission.
The U.S. Defense Advanced Research Projects Agency (DARPA) and NASA have conducted a successful test of their robotic in-flight refueling system. An F-18 fighter, modified to operate without a pilot, w as equipped with the new refueling software and ahrdware, and was able to successfully refuel in the air.