User blog comment:Xilinoc/Ch. 573 (Let Unohana return plz)/@comment-1659214-20140320180554/@comment-5693502-20140321104129

Yama's death wasn't completely BS. It was a calculated move by Yhwach. Why let a guy who could single-handedly eradicate every Sternritter live, when you could just exhaust him and take him out of the picture entirely.

And as for Unohana, she said it herself. She died to power up Zaraki. There's your reason. Zaraki is the Gotei's trump card. Sacrifice your pawn to get a better piece (although Unohana is a lot stronger than your average pawn).

Though I do hope that everyone that's been stated to be dead, stays dead, regardless of how great of character they were (or weren't). It's a huge war in the last arc, people are supposed to die.