When Toph came into the picture I thought to myself "sweet, Zuko will join them, then some surviving airbender will join, maybe sokka will leave or get killed, and then PERFECT! we will have one bender of every element,??excluding the avatar, in the Gaang!"
Now??Toph's future seems uncertain, but if the Guru is an airbender and joins the gaang, and of course assuming Zuko joins, it would be like the unstoppable fivesome!??