Having had quite enough of her constant yammering--always, Oh, the Doctor would know what do to this, and The Doctor would never do it that way that--Torchwood chucked Rose into the void with the semi-sincere hope that she would make it back to her original universe.
Coincidentally, this was at the same time that, having grown thoroughly sick of hearing the same sort of nattering about Rose, Donna pitched the Doctor into the void as well.
And then she went off in the TARDIS and had lovely adventures in Time and Space.
Donna was a much better navigator than the Doctor had ever been.
2 - Mean
Rose cried.
At long last, it was him! Her Doctor, just as she remembered him, all floppy-pointy hair and pin-stripes. Trotting beside him was a very handsome blond man and a green-skinned woman with large breasts and small clothes.
"Oh, you're going to love this," he said to them.
His companions nodded enthusiastically.
"Doctor!" Rose cried, as the little group passed her.
He stopped and stared.
"It's me," Rose cried. "I've found my way back to you!"
"Errr, right." The Doctor squinted. "I'm sorry; what was your name, again? I'm rubbish at names."
Rose cried.
3 - Likely
"But you haven't been alone all this time, have you?" Rose snuggled closer to him as they walked.
"Well," the Doctor said and pointed.
A scowling, ginger-haired woman stood in front of the TARDIS.
"Where the hell have you been?" she screeched. "And who's this you've got with you?"
Rose looked up at the Doctor, horrified.
"Oh, Rose," he said grimly. "You're going to be so annoyed."
4 - Dark
"Mickey?"
"Dead."
"Jackie?"
"Dead."
"Pete?"
"Dead. And my baby sister and Jake and all of Torchwood and most of the planet. All dead." Rose squinted up at him, her eyes bruised and swollen to slits.
"Oh, Rose," the Doctor said. "I'm so sorry. I'm so very sorry."
"You can take your sorry and rot in hell." She coughed wretchedly and spat a mouthful of blood as red as the dress she wore. "You and my Lord Saxon, both."
5 — Fairytale
In the end, it was far more simple--and far more glorious--than either of them could have imagined. The TARDIS, the cleverest and most intrepid ship in the universe, found a wormhole that would allow the safe crossing between universes. And cross, the Doctor did.
He found her in Cardiff, working for Torchwood. She was eight years older, her figure a bit more trim and her hair a bit more brown, but when she saw him, her smile lit his world like the sun. The Doctor and Rose were reunited, and it was like nothing had ever come between them.
And then they went off in the TARDIS and had lovely adventures in Time and Space.
The Doctor was just as terrible a navigator as he'd ever been.