Danzo went all out on Sasuke and when he realized that he was under his genjutsu it was already too late for him. But He had another trunk card up his slave it was eye power of Sharingan. His main target was Uchiha Madara, he wanted to take his under genjustsu but to do that he must eliminate Sasuke. At his condition he was not able to do both and trying desperately to escape he took his decision of taking hostage of Karine but unfortunately for Danzo, Sasuke was consumed whole by his hate and insist on revenge. Sasuke cut through Karine and hit Danzu right into his heart. Danzo in his last moments took a last shoot at Sasuke and Madara by trying to pull them both with in claws of death.
Danzo near his death saw flash back from his past where he was teaming with 2nd Hokage and 3rd Hokage along with his leaf Ninja comrades. They are being persuaded by highly skilled trackers of Kinkaku unite. To escape from this situation in the time of war 2nd Hokage decided to be decoy while the others make run for it.
This might be the reason of death of 2nd Hokage. Don’t you think when he left he made Hiruzen 3rd Hokage.
