Craig: Whether Penn Central happens there is still going to be an overabundance of lines serving the northeast and midwest. The de-industrialization in that area is still going to happen. Agnes is still going to wreak havoc and the oil crisis is still going to hit. So to that extent I agree. Plus without Penn Central's collapse it is possible some of the regulatory and tax changes that helped revive Conrail, and aided other lines, would not have happened. However I think the larger N&W shows that it would have been possible to combine certain roads in the northeast-midwest into a financially viable system.
Stix: Sorry, typing error. I meant Chessie-NYC. IIRC the discussions on the PRR-NYC merger started in the late 1950s, while Southern did not take over the original Norfolk Southern until the early 1970s. If we assume no Penn Central that opens up the possibility of alternative combinations happening in the 1950s or early 1960s, before Southern took over the original Norfolk Southern.
Don: I agree. However the map would probably have ended up much different, with true U.S. transcontinentals likely. It does not require a significant historical rewrite to have Burlington Northern trains showing up in Savannah Georgia even with Penn Central.
David: I believe regulatory hurdles delayed the Penn Central merger. Makes me wonder how the SCL merger was pulled off.