Like a few of you have also said, I believe that Tsunade was fully aware of the approaching Sand Nin. She most likely (and covertly) set up an Alliance with the Country of Wind / Sand Village. She most likely threatened them into an Alliance, as some form of repentance for foolishly invading Konoha. Being superior to the Sand, their [the Sand] shinobi probably now fall under the orders (when necessary) of the current Hokage.

On another tangent, we have seen tons of (supreme kick-ass) surprise returns .. all we need now, for more battle-irony, is for Sakon & Ukon to somehow destroy Kankuro's puppet. Needing another person to aide him in battling the two Level 2 Sound-Nin .. Shino arrives. That way, all teams would be composed of former opponents.

On a final note, Kishimoto is surely delivering the fan-favorites .. Namely, my favorite .. Lee! Wewt ..

Ninja vanish!