This happened to my in-laws DFW-NRT, albeit due to IRROPS. They were re-booked in W for flight the next day but it was overbooked (no seats available). They ended up in last row of coach (they have no status and didn't really realize enough what was happening to push back/ask for alternatives). Ultimately they received refund for difference between Y and W which wasn't much because I got W at a low price.
I would be prepared with all kinds of alternatives.