Personally, I believe even the KH section will still be running. Maybe not as actively, but there will always be someone who just got the game and needs help. And there will also be discussion of the games plot, as well as anything else KH related. And of course the other boards will still be up for discussion.
Just because something is over doesnt mean it is forgotten. One of the most famous lines around today is about 9/11, "Gone But Not Forgotten". And hell, Blink 182 stopped making music as they went their seperate ways, but people still listen to and discuss their music.
So yea, this forum will be fine. And you wont have to worry about that anyway for the next 4 to 5 years.