Square Enix has made it clear that Kingdom Hearts 3 will come with mature content to cater to the fans that are mostly adults by now. Also, the highly anticipated game will see the downfall of Xehanort via the big war.
With that being said, it won’t make sense if there is no death happening on the good side. While it is going to be sad to see some loved characters dying, it is an element that must happen to make the game more emotional and dramatic, instead of something anti-climactic.
While no names have been officially revealed, we feel that it will involve one of the three Wayfinders. It might sound harsh but Terra will make the perfect candidate for death.
Terra is a character that has been constantly been possessed. Perhaps, in Kingdom Hearts 3, the fellow will lose total control which gives Sora no other choice but to end Terra once and for all.
On the other hand, Sora too could get killed in action. Of course, Square Enix has already confirmed that the main character will be living in future titles so this may seem unlikely. On the other hand, there is a possibility where Sora dies and comes back to life with the knowledge to kill Xehanort.
Either way, death is bound to happen in Kingdom Hearts 3 and there is no avoiding it. We can trust Square Enix to surprise us with this element, thus enriching the emotions in the game.