The answer depends on the terms and details of the sale. All that stuff is negotiated pretty heavily before anything changes hands.
A) Railroad ABC buys all the lines from Mattawamkeag to Ayer, and buys all the PAR-owned rolling stock, including the business train. Railroad XYZ buys PAR's stake in Pan Am Southern.
B) Railroad ABC buys all the lines from Mattawamkeag to Danville Junction, and buys all of the PAR-owned freight cars but doesn't buy the locomotives or the business train. Railroad XYZ buys all the lines from Danville Junction to Ayer, and buys PAR's stake in Pan Am Southern. Locomotive leasing company 123 buys all the PAR-owned freight locomotives. Tourist railroad 789 buys the business train.
C) Railroad ABC buys everything. Railroad ABC puts the business train on the auction block. Auction bidder 123 buys the FP9s. Auction bidder 456 buys the observation car. Auction bidder 789 buys the other three cars.
...and so on and so forth. You get the idea. Lots of possibilities!
Pan Am Railways — Boston & Maine/Maine Central — Delaware & Hudson
Central Maine & Quebec/Montreal, Maine & Atlantic/Bangor & Aroostook
Providence & Worcester — New England — GE Locomotives