The allies do not have the luxury of assuming that this is the case. And there are significant worries about an australian invasion, they have to plan for it. If the japanese get new guinea, they're going to be able to threaten the supply lines of australia. It's important to assume that both are involved in any planning or operations. This area is going to be like the black hole of the pacific theatre for a while,. sucking in men, plaing ship supplies from both sides.