Like the others (CAF comes to mind), Nippon Sharyo will be back, briefly, if a big enough contract is offered. Unless things are ridiculously rigged (which has happened) re. Buy American, they could do it like they did back in the Fourth Age of Middle Earth, when Caltrain was just starting up and needed to replace all the old SP stuff with shiny new push-pull cars patterned after Metra's. Carbodies were built in Japan, shipped to a pier in SF where they were mated with running gear and interior parts mostly made in the US. One-shot, minimize facility cost, then leave. Some of those cars are still running, after almost 40 years. CAF did something similar for Sacramento's early-2000s light rail cars: set up an assembly plant at McClellan, assembled the cars using Spanish carbodies, and left with no other immediate work prospects. The only companies that seem to have made a go of US transit production over the long term are Siemens and Alstom, both of which do Real Railroad stuff as well as transit.

The problem with the one-shots is that they may be low-bid for construction (though we all know how that works out with politix and change orders), but there's little capability or desire for after-sale service. That leads to the companies that do stick around (aforementioned Siemens and Alstom) picking up a nice line in support/rehab for all sorts of stuff, not just their own. And being the only companies that can manufacture almost entirely in the US, they get a leg up on Buy American.

As Bob says, oh well...