The current SCOTUS majority isn't afraid to overturn 50 year old precedents. Given they overturned Roe v Wade, why not Train v City of New York too?
But they don't strictly speaking have to overturn it, just limit its scope of application somehow. For example, Train was about grants to the states – SCOTUS might rule the Congressional Budget and Impoundment Control Act of 1974 unconstitutional, and decide that the President has the right in general to impound appropriated funds, but they also might follow Train in carving out an exception to that general right for grants to the states.
But they don't strictly speaking have to overturn it, just limit its scope of application somehow. For example, Train was about grants to the states – SCOTUS might rule the Congressional Budget and Impoundment Control Act of 1974 unconstitutional, and decide that the President has the right in general to impound appropriated funds, but they also might follow Train in carving out an exception to that general right for grants to the states.