This would only happen if Microsoft somehow screws up Halo 5. I really don't see this happening. I expect UC4 to sell about 7 - 8 million copies, while Halo 5 should do about 10 million.
So far the best selling Uncharted game on the PS3 (UC2) sold 6.3 million copies, while the best selling Halo game on the 360 (Halo 3) sold 11.9 million.