User blog comment:IamJakuhoRaikoben/Chapter 330: Zirconis' Magic, Review./@comment-5580383-20130512055455/@comment-7418318-20130512062802

Unohana never fought even once in the entire series (lost the will to fight or some bullshit like that), so losing her "battleprowess" is of no consequence.

WIth so many fighting Shinigame dying and barely (if any) of 4th devision dying (they were kept out of the fight after all) the ratio between healers and those who need healing has shifted in a way that the loss of a single healer isn't that much of a blow really, even if she was the best.

So in short I absolutely agree with FTGM. While it was a bad decision from the author, in-universe the benefits are likely well worth the cost.

Even though it reeks of desperation. Because what will happen once the Quincy are defeated? It's quite possible that Zaraki will go out of controll and slaughter hiw way through Seireitei and with Yamato dead, noone could stop him.