theres alot that we might not be able to see in the background
if nvidia launches at a high price, amd would not lower unless they see stock start piling up. what the competition is doing is not their main reason for pricing, its their own supply and demand. naturally having more cards in the high end does mean they will probably sell less, but for all we know they will still sell every card at the high price, even with competition out.

if nvidia comes out and sets their prices low, it could be because they believed they couldnt clear their stock at the higher prices, which might be due to having great supply quantities. or they are doing it knowing they earn less per card, but also undermine the competition and forcing them to earn less per card.