So about Nuka's death...

[Thegeni99]

vegetative state?

[TheLionPrince]

If you want to look deeper into why the writers wanted to kill off Nuka, then, you take a look at the story material that inspired their story.

In this case, Romeo and Juliet inspired The Lion King II. Nuka is very similiar in terms of Tybalt, as both characters are very violent and wish to battle a member of the opposing family, and when they do, they die. Their deaths in both stories heightens the dark tone in the respective stories.

So, in Romeo and Juliet, Tybalt (and Mercutio)'s death only worsens the feelings the Montagues and the Capulets have for each other, which mades it harder for Juliet to get to Romeo. While in TLKII, it causes Zira to really go after Simba and the Pridelanders, which leads to the battle that is the climax. The climax then leads to the resolution with the Outsiders joining the Pridelanders as one. So, Nuka's death was essential to the development of the story.

[Saffyminty]

Well I've never thought much of the meaning of his death, but here's what I've come up with...
Alrighties, The writers obviously wanted more drama and stuffs but lets think outside the creators box and into the actual TLK universe;
Nuka has always fought and tried to get his mother's attention and for her to love him, but she doesn't ever retaliate. It is Nuka's 'time to shine' when Simba is vulnerable, because if he could get a chance to kill him all the Outsiders (especially Zira) would adore him, and he would be more respected than Kovu! So yes that is why he did what he did.
After he dies Zira is sad and so is the rest of the Pride. I really wonder why, I don't think anyone would've liked him and the Outsiders were a very tough and un-emotional pride.
When Zira blames Kovu and says "You killed your own brother!!!" She's upset that her young son 'killed' her older son. Very hypocritical. For Scar killed his older brother...hmm...!!! Get's you thinking, and that maybe made the other Outsiders thinking later (Vitani mostly) becuase she's the first one to side with the Pridelanders and then the other Outsiders quickly followed her. Maybe they are a bunch of cowards and they want someone to do something first before they do it.
So yes. Nuka's death sends the message that even Zira doesn't agree with brothers killing brothers. Maybe... I'm not sure that's just what I've come up with!