Kuroo doesn't meet his demise in the manga. The plot doesn't involve his death. He continues to play an important role and contribute to the story's development.
One possible reason could be that Tsukishima is under some sort of mind control or influence from a more powerful and malevolent force. Maybe he has been deceived into believing that Ichigo is a threat to something he holds dear.
One common theme is friendship. Their strong bond is often explored in various ways, like how they cheer each other up when one is down. Another is growth, both as volleyball players and as people.
Ichigo might initially be in shock. He could be unable to believe that Tsukishima, who might have been a friend or at least an acquaintance, has turned on him.
Tsukishima's back story has a lot to do with family influence. His brother's success in volleyball was a big factor. He was in his brother's shadow for a long time. As a result, he was hesitant about volleyball. But as he grew in the Karasuno team, he started to find his own identity in the sport, separate from his brother.
Sure! 'The Courtship of Bokuto and Kuroo' is a great one. It really delves into their unique friendship and how they support each other both on and off the court. The characterizations are spot - on.