IMO the discontinuance of the National Limited was one of Amtrak's biggest mistakes. It was the only direct single train route from New York to the cities of the Midwest, making stops at Columbus, Dayton, Cincinnati, Louisville, St Louis and Kansas City.
Even if Amtrak hadn't discontinued that train in 1979, I don't think it would have lasted much longer. The infrastructure was deteriorating and large sections of the ex-PRR/ex-PC/Conrail route along with its B&O predecessor route were abandoned later.
It's a route that will probably never come back due to lack of infrastructure. Especially the Pittsburgh-Columbus connection.
Example 1: original B&O routing (did not serve Columbus) is severed west of Parkersburg, WV
Example 2: Amtrak routing (following PRR's Spirit of St. Louis) through Columbus: the line (ex-PRR/ex-PC/ex-CR Panhandle Route) is severed between Pittsburgh and Columbus
Example 3: the B&O routing from Pittsburgh to Columbus that's visible on the National Limited map above is also severed.
Intact lines:
1. CSX still has an ex-Conrail line from Indianapolis to St. Louis and uses it for intermodal traffic. This line was spliced together from cherry-picked PRR and NYC trackage.
2. Most of the ex-NYC "Big 4"
3. The ex-B&O line between Cincinnati, Louisville, and St. Louis
Remaining options:
1. extension of the Cardinal: The Cardinal's already slow so this isn't a great idea
2. ex-NYC Knickerbocker/Southwestern Limited: this was historically a slower, less-direct route and skips Columbus. The Water Level Route is intact along with the connections to Indianapolis (active intermodal route as I mentioned above).
3.) Some hybrid of the Capital Limited/Broadway Limited/Three Rivers type routing west of Pittsburgh: run the ex-B&O (Chicago) line and switch off at Greenwich or the ex-PRR Fort Wayne Line and switch off at Crestline. The direct route won't serve Columbus. A more circuitous route can serve Columbus and Dayton but has to dip down to Hamilton before coming back up to Indianapolis. Or it can continue to Cincinnati.