I'm well aware that it's a couple hundred trucks to replace a single train. I'm not sure you understand that this is what already happens. Rail carries around a quarter of freight ton-miles in the US. Trucks carry much more than that. All of the stuff that isn't bulk, time insensitive freight, or anything that surges in excess of the carefully scheduled rail capacity already has to spill over onto trucks. That includes things like disaster recovery shipments, unusual seasonal demand, and so on. There's also a population of truckers that work these temporary jobs, as well as a certain level of excess vehicle capacity in the fleet carriers to service it, plus whatever truckers can be pulled from other work to meet the demand.

Anyone looking at massive losses will pay the sticker shock to put it on trucks. Anyone who can afford to shut down instead will wait. That's the system working as intended.