Well, the F-51 wasn't withdrawn from second-line U.S. service until 1957, continued in other roles until 1968, and was in front-line service in some Third World air forces, particularly in Central and South America and some Asian air forces, until 1984. The Dominican Republic was the last full-time user. In fact, the U.S. Air Force was selling remanufactured F-51s under the Military Assistance Program between 1968 and 1972. Its last combat use was in 1969, during the "Soccer War" between El Salvador and Honduras, and the F-51's last combat loss was in 1965, again in the Dominican Republic during "Operation Power Pack."
I suppose that in the world of DCS, the F-51 could still have a place vs. helicopters and subsonic aircraft. It'd be at a real disadvantage avionics-wise, with no radar warning gear. But then, the Ka-50 seems to get by without that, and the Mustang's six .50s and rockets would still be a force to be reckoned with in the air-to-ground game. I'm willing to suspend disbelief, just not enough to buy it. Though I'd love to see some screenies with Central and South American liveries from the 1960s and 1970s.