I would tend to think they will come down some at least, they always do. How much might depend on whether Nvidia comes out with other cards or lowers the price on the GTX470/80 so there can be a price war of sorts.
FYI if you can handle overclocking the HD5870 isn't really worth the money. The HD5850 is $100 less and OCs an absurd amount(40-50%.) The HD5870 OCs to the same speeds but when running at the same speed that card tends to be only 5-6% faster than the HD5850. Not nearly worth $100 more imo.