I don't have an answer to your question, however, here is one thing you can do:
Go to Amtrak's website and try to make a reservation on the Coast Starlight from, say, Klamath Falls to Salinas. If they show you as getting off in Oakland and then a bus to Salinas, then you know the detour is still a go. If they show you riding the train the whole way, then no detour.