Mickey saves the day!

[McLovin']

When all hope is lost. When the bad guy is seemingly destroying you. There comes hope. A mouse comes out of nowhere and takes your place.

Why?

[Tavrobel]

Because if Sora dies, then the game is over. No point to continue, because Sora is either:
a) unable to save the universe
b) his soul can still be manipulated Organization XIII
c) his Nobody will no longer find him
d) Namine and Kairi will be really pissed if Sora is dead
e) if his Heartless recedes back into the darkness, then Sora will kill everything
f) Mickey will be pissed, because that's one less Keyblader
g) Donald and Goofy will be dead also

[NeoCracker]

Because Mickey is a pimp like that

[McLovin']

But why?

[Tavrobel]

corncracker and I already answered that.