Somehow, I´m not surprised Kuro could turn around the situation, it was already hinted and showcased throughout the series, the gap in experience between Kurosensei and the 2nd god of death and Yanagisawa, in their best of skills (the inteligence department, the hitman tactics (all the 2nd god had superior to Kurosensei was him cutting and removing his own face off and lets be honests he did this not case it was needed to survive, but case he wanted to attain "new skills")) (Kurosensei was smart enough to trick Yanagisawa during his own experiment, how could he not caught him off guard and unprepared twice with such gap?

).
The second god of death was made purely to overwhelm Kurosensei in his basic traits thanks to the antimatter tentacle op. bonuses, but the 2nd god of death lacked the experience necessary to surpass Kuro´s who had control and was used to his new body for months, Yanagisawa´s support, was a good strategy but he couldnt take the frontlines against kurosensei and made the 2nd god dependant on him for action that was a terrible mistake, case he got overconfident and Kuro turned the tables up, what Kuro used for that though, was quite shocking and quite unexpected indeed.
Now about Kayano, I think she might survive, Kuro couldnt save her sister way back case he didnt try and learn any medical skills whatsover, now it´s diferent he had lots of time to master that and more, I just have doubts about what will happen to 2nd god of death, I thought he was already dead but there was a saying at the end of the chapter that implies he might still be alive after that beam
http://www.mangahen.com/assassination_classroom/174/17/, didnt expect that one.