DA:
You come by your name honestly.
I don't know what items this hypothetical passenger is ordering. I only know that it must be assembled into one or more meals in the dining car kitchen, and transported as quickly and safely as possible to the consumer. The chef will be busy. The wait staff will be busy. I don't know whether the passenger is capable or not. If the passenger drops it midway (hopefully not on himself or another passenger), then the whole job has to be done over and the mess cleaned up. As an Amtrak employee, I was always too lazy to want to do a job twice when it was quicker and easier to do it once; I was also too safety conscious to want to invite trouble.
Since I wasn't a lounge car LSA, I'll choose not to address the flaming-hot pizza problem.
Your scenarios all refer to whether the passenger or the employee should do the job. I have said it's the employee's job. If the employee is "MIA", that means he's either busy with some other aspect of his job, or he's a poor employee. If that happens, some other employee should be brought into the situation to do what is needed. I'm not on this hypothetical trip with this hypothetical passenger who has a hypothetical SCA who is hypothetically MIA. If I were, I might be able to make more specific recommendations.
Many of the services provided on the train will be provided in a specific way because that is what is most appropriate in the specific circumstances. Under slightly different circumstances, a very different approach might be more appropriate. I can't give you any ironclad, immutable rules that will cover every contingency. In my career, I made thousands of round trips and my duties and challenges probably weren't exactly the same on any two of them. We have brains so that we can use our judgment to figure out what is likely to be the safest, fastest, and most efficient way to provide the service that is needed. I have presented some guidelines that have been useful over the years. If you don't like them, you can relax because I don't work there any more.
I think I'll just leave it right there until the discussion starts going in a more profitable direction.
Tom