Thats simply speculation at this point, even going from the recent interview we saw that AMD expects Fermi to be faster on a single chip vs single chip basis. They will of course be pleasantly surprised if the situation is different.
A price war requires at least one party which wishes to engage in one, since there are of course only two parties. In this case Nvidia has no incentive to engage in price based competition and AMD aren't exactly the most profitable company in the semi-conductor industry. If theres to be pain for Nvidia it will come from an uncompetitive Fermi chip in the short term and be purely self inflicted and if theres pain in the longer term it can only really likely come from either R9xx releasing this year OR an early die shrink of the current AMD lineup.
At this point im not willing to call Fermi uncompetitive nor AMD willing to give up much needed profit for market share.