A long time ago, Naughty Dog said that, if they were to make a sequel, it would be with a different set of characters.
It's almost guaranteed to get a sequel. With scores like it's got and the hype on the web, Sony will demand a sequel.
I could see it, there's always more stories out there. Of course it won't be Joel, we don't even know if Joel could have another story. We don't know what happens in the end of this game, I thought I did, but apparently all those spoilers on the internet aren't true. I've been watching a walkthrough, and I've gotten to the E3 area, I really want to continue, but I've decided to stop and just wait till Friday. I haven't even seen all of it before that, I'm skipping around. Amazing game though.
I would like to see a sequel that follows just one character, rather than two. It will make the game even more intense and you don't have to worry about the friendly AI in your way. They can call it, The Last of Me.