Shōgun Episode 10 Reaction "A Dream of a Dream" 

Crimson Sky will lead to Ochiba's death. I don't think Mariko would have wanted that.

@@MustardSkaven that future is after the defeat of Ishido. And it was because Ochiba and his son was gathering supporters to take back power. In the moment, Ochiba secured her life and that of her son, by pledging not to give their Samurai and banner to Ishido. She finally saw what Daiyoin-sama was warning her about Ishido, he would not have been able to consolidate power and usher peace the way Toranaga can because he [Ishido] would just control everyone through coercion. She simply realized that she bet on a losing horse; corrected herself in the last minute; and bought time for herself. In the end, she never became Toranaga’s ally, which sets up their later conflict and the end of the Taiko and Ochiba’s line.

@@khaii13 So Ochiba and the heir die cause Crimson Sky happened. If it hadn't happened, they would have stayed alive.

@@MustardSkaven that’s a leap, but I’ll bite. If it didn’t happen, Mariko would not be able to fulfill her loyalty; there is no Tokugawa victory; and even if Ishido won, Japan would have been divided in centuries civil war. Not to mention, in ep2, even the Taiko was saying the vultures were circling. So it is not out of the question that, if crimson Sky did not happen, and Ishido marries Ochiba, that Ishido would have the heir and Ochiba killed once he gets his own heir through her.