#3 - I would agree that Mitsubishi and Isuzu are the most likely candidates for dissolution. However Lexis is just a rebadged Toyota as is Infiniti is just an expensive Nissan. Both of those premium brands are wholly owned subsidiaries of their respective parents. So I would not expect them to disappear.
Isuzu and Mitsubishi make trucks. I do not see them leaving that market.
Don’t forget Acura, which is Honda’s “premium” brand. Honestly, I see so few Acura’s around I don’t know how/why Honda keeps that brand afloat.