The SR-71 did have a replacement You dont retire a plane that was basically invincible it was shot at thousands of times and was never hit. That type
of plane still has a role just look at the U2 it is still flown. Amazingly no one made a stink when they retired the SR-71
They built a plane that was not only flies high and fast but is also use stealth. So now not only cant you shoot it down but you dont even know its
there now.
When we find out about this plane it will most likely be replaced with something better. Perhaps a space plane.




The Technology might be new but the concept and role of the plane will still be the same.