I have an idea for part 09
Many say that Shadow is the one who'll save mario and co.
why not make it like this:
Back at Sonic's world, the master emerald is still there.
but all Sonic's friends are dead (including Knuckles). Tikal (Master Emerald's spirit) uses the power of the Master Emerald to revive Knuckles as soon as Sonic and Shadow leave to Mario's world (Although the Master Emerald has infinite power, we'll lower it so it leaves the balance between both worlds).
Now revived, Knuckles uses the Master Emeralds' remaining power to revive Tails and send him to the world Sonic left to.
Tails doesn't arrive at the same town but at somewhere somewhat far form there and starts building a new Tornado (airship) to search for sonic.
Tails only found Sonic at the battleship.
if anyone thinks he can add-improve this idea please feel free to.