I can only hope that lecture thing wasn't empty words but things will come back to bite both of their asses eventually. Because immortality with unlimited chakra is bullshit. If this story has any sense, Oro would have known that and not used it precisely for that reason. Of course he still has the technical weakness of becoming a slave if somebody sticks a kunai with a paper slip into his neck. But since that would kill a normal person, it's not really a weakness to speak of. However, Madara didn't have much choice, so he would have done it even if it carried some major flaw, like it should.