Yeah, we ahould be concerned about our offspring millions or billions of years from now.

Extract:

"When the planet goes cold, it'll lose its magnetic field, which shields Earth from harmful cosmic radiation. At that point, Earth would become a sterile, uninhabitable rock."

Not so fast. That harmful cosmic radiation can only destroy life on the surface. We now know that bacteria thrive many feet/meters below the surface. Also, sea floor vents demonstrate they can provide organisms with chemical sources of energy completely unconnected with solar radiation. Such pockets of life may exist on the moons of the outer planets if they are geologically active and have oceans. AFAIK, Europa and Enceladus are candidates.