Diesels will be around for a long time. The reason nat gas is cheaper is because there are no road taxes on the fuel - and how long do you think it will be before that changes? Revenue starved governemnts will be all over that as soon as nat gas adoption goes mainstream. The other big issue with nat gas is the relatively short range of the truck. Same packaging size gives you 1/4 the range of diesel. LNG or CNG - same issue.No, there hasn't been much of a market for passenger diesels in the U.S. And I don't expect there will be. For over road rigs and heavy equipment, sure, but not for family passenger vehicles.
And there is a move on now to convert our diesel truck fleet over to natural gas which we have in abundance of about 200 years supply. And with the BTU content it is about half the price.
I could see dual gasoline and natural gas vehicles but I view diesels as a dead end street in the U.S.