If the worst does happen, I believe that will present great opportunities for enterprising entrepreneurs to fill the vacuum with some kind of alternate service...Such as an 'app' on your smart phone that would let you choose from an excellent menu, order ahead, and have hot or cold meals delivered to you right at the platform on some of the stops enroute. Such a plan could work, even if the train were delayed. That would work out better than having scheduled meal stops at stations, like in the Harvey House era. And it would offer much greater choices...
There are a few problems I see with this premise.
1. Even when Amtrak is on-time at the final terminus they can still be off by hours at several midpoints along the route. Not knowing when your food will be needed or how much time you'll have to deliver it would make such a service rather inefficient.
2. In many locations the train and platform area are off limits to vendors and/or under the control of a third party. That would make it difficult to serve passengers quickly and efficiently.
3. The vast majority of Amtrak's network receives two trains or less per day and in some cases as little as once every few days. If only a few people order food on a given train do you deliver it at a loss, cancel the order(s) due to insufficient demand, or raise prices to the point that even one single entree has made enough revenue to pay a driver to sit and wait for the train to arrive and for the customer to walk off premises to collect it?
4. If anything goes wrong there probably isn't enough time to make it right before your customer is on the move again. That could mean a relatively high ratio of displeased customers, an excessive number of negative reviews, and difficult to defend charge-back requests.
5. From a commercial business perspective you can't simply start with a burrito lady and just scale up. The reason the burrito lady remains viable is because her whole business is under the table. If she had to maintain a licensed kitchen, hire employees and pay them a legal salary, collect taxes and pay an access fee to use the station facilities, and cover all the other usual business expenses she'd never make a profit.
If there were one location where a third party could make and sell food for eating on board Amtrak, and be able to provide that food in a timely fashion directly to passengers, it would be Chicago Union Station. The problem there is that Amtrak owns/controls the relevant parts of the station and probably wouldn't be willing to allow a third party to cannibalize their own dining service.
Amtrak's "core customer" is not the long distance passenger that uses a dining car. 88% of Amtrak passengers ride trains that do not have dining cars, and of the 12% that ride trains with a dining car, some significant percentage of them do not use it. If about 1/3 of the passengers on a long distance train do not use the dining car, that reduces the utilization to about 8% of all Amtrak customers. Thus, for about 92% of Amtrak's customers, changes in dining car service will have no impact on their on board experience and perception of value.
If anything abandoning the long distance network will probably make Amtrak stronger financially. Which is why those of us who live outside the inward focused commuter corridors are rightfully concerned whenever service or amenity levels undergo yet another supply side revision. Personally I think some of the reasons so few people use the dining car is because the food quality is poor, the cost is high, the service is slow, and the staff are rude. But I guess you can't teach a dead horse new tricks.