The Doctor would regret the offer.
First, I'd make sure I had a tent and a placard. Then, I'd coolly inform him that I don't want anything to do with any of the future daleky time war idiocy, and I'd insist instead that we spend a weekend at Woodstock, followed by the opportunity to march in the civil rights movement and hear Dr King's "I have a dream..." speech.
Then, after that, go back a bit further and meet the Earl of Rochester, John Wilmot, preferably before the syphilis. I'd probably insist on Harkness accomanying us there as bait.
Oh, he'd regret asking me all right...