Together or not at all.
I will always remember when the Doctor was me
“And do one more thing for me. There’s a little girl waiting in a garden. She’s going to wait a long while, so she’s going to need a lot of hope. Go to her. Tell her a story. Tell her that if she’s patient, the days are coming which she’ll never forget. Tell her she’ll go to sea and fight pirates, she’ll fall in love with a man who’ll wait two thousand years to keep her safe. Tell her she’ll give hope to the greatest painter who ever lived, and save a whale in outer space.
Tell her, this is the story of Amelia Pond. And this is how it ends.”
via Bleeding Cool:
As it happens, the introduction of Amelia Pond was not contingent on the arrival of the Eleventh Doctor. Speaking to Doctor Who Magazine, Steven Moffat has explained what his basic story arc for series five would have been if David Tennant stayed on and Matt Smith not been recruited.
Here’s his explanation:
I only had the roughest idea. Had David stayed for one final year, it would certainly have been his last, so my pitch was that it would start with the Tardis crashing in Amelia’s back garden – as now – and a terribly battered and bruised Tenth Doctor staggering out.
Amelia finds him, feeds him fish custard (no that was for Matt, it would have been something more Davidy) and generally helps him. But we, the audience, can see he’s in a truly bad way. Dying maybe. Eventually he heads back to his TARDIS, and flies off.
But when he returns – many years later for Amy – he seems perfectly fine, and indeed doesn’t remember any of those events…And of course over time, we realise what we saw was the Tenth Doctor at the end of his life, about to regenerate. Events that we return to in Episode 13…
One of the most interesting things about this are the implications for the relationship between Eleven and Amy, even Rory and River.
Either Eleven would never get to meet Amy and Rory, which would most likely have changed the River Song storyline profoundly, or he’d meet them after they already knew Ten.
Young Amy: …Funny.
Young Clara: …You’re sad.
Doctor Who Series 5: The Eleventh Hour
Yeah. Amelia. Little Scottish girl. Where is she? I promised her five minutes, but the engines were phasing. I suppose I must have gone a bit far. Has something happened to her?
based off this
The Eleventh Hour (5x01) / The Power of Three (7x04)