Black zetsu could only take over obito because half of obito was already white zetsu. the more you knowwwwwww
85% of nagato's body was covered in madara's will (black rod)
Yes he could of done the same, if nearly dying like Obito.
Have Black Zetsu take over Nagato when he used Rinne Tensi? I know Madara was dead at the time but he could of planned it as a fail safe.