Fun episode. I loved the puppetry scene, but the bi-generation feels a bit weird to me. Interesting if they want to keep 14 around, or if he’s gone after the Christmas special.
I figure, considering David Tennant's age, and past willingness to reprise the role, and the age of the show, it's a safe bet he shows up a few more times, even if they had killed him off.
That's the fun of shows like this - literally nothing is off the table. It's like kids playing games at recess, making up rules as they go. There's a bit more to it than pure "lawlessness", but the rules can always give way to fun. I love it.