NOTE: It's a short story about the aftermath of the Kraang Invasion (The Invasion!) My theory that Leatherhead and Splinter was still alive after fighting the Shredder.
In the aftermath of the Kraang Invasion, Master Splinter was still unconscious in the sewers. Karai saved his life and was protecting him. It was until the water was bubbling and out of the water was Leatherhead. He was an aid to Master Splinter and a good friend to Leonardo, Raphael, Donatello and Michelangelo. He remembered how he saved the Turtles from Traag, the Turtles saved him in Dimension X, and saves Master Splinter from being attacked by the Kraang and Shredder. All that he knows is going to wake Splinter up. "Great Splinter, can you hear me?" said Leatherhead, poking the rat's shoulder.
Splinter opened his eyes and sees Leatherhead. "Leatherhead, I'm glad you're still alive. How did you survive?"
Leatherhead looks at the water. "After the Shredder throws me down, I manage to swim underwater. Then, when you are here, I saw a snake saving you."
Splinter recognized the snake from somewhere. "That snake... is my daughter."
Then, Karai appeared, in her snake form, out of the water and changes into a human but with green snake eyes. Splinter turns around to see Karai. "Miwa... Thank you for saving me."
Karai nodded and Master Splinter has to go find the turtles, April and Casey. "Can we help you find your sons?" asked Leatherhead.
Karai managed to remember the turtles. "Leonardo..."
Master Splinter nods. "Yes... We're going to find my sons but first, we have to get past the Shredder and the Kraang."
"Then we need to get out of the sewers," said Leatherhead.
Karai agrees with Leatherhead and Splinter and changes into her snake form. Splinter sets off with Leatherhead and Karai to find a way out of the sewers, getting past Shredder, his army and the Kraang and hoping that he will reunite with his sons, April and Casey. The turtles will hope that the master will reunite with them.
ANOTHER NOTE: For those who watches the TMNT 2012 Season 2 Finale "The Invasion," How many of you want Splinter and Leatherhead back in Season 3 of TMNT 2012?