Even then, I have to imagine we could get arrange a knowledge transfer from our vassals that do have functioning mass transit (a decent chunk of european NATO countries, Japan, maybe South Korea).

there's definitely been consequences to de-industrialization, but I think it's less of a matter of the entire labor force having to re-learn skills they forgot and more that there are simply fewer people with the necessary skills, and they'll have to do more work, as a result.