It is Possible that that Brazil might be the country that Portugal's colonies turn to. In fact Brazil might seek to dominate these colonies, at least the ones in Africa.
I would not imagine them surviving terribly long. Portugal's African colonies weren't terribly populated by Europeans at this juncture of history. With the annihilation of the metropol, there is no one to support these colonial ventures, and quite frankly few nations would worry about such things when they are busy trying to stay alive. Brazil could conceivably keep Angola, given the long history between the two states. That being said, I have to reiterate the fact that portugal got wiped out by the Atlantic impact as nearly the entire nation got hit by the brunt of the waves.