Ok we're ending random speculation territory but it was widely reported that the Google Maps agreement expired this year so there was no huge decision about when to release -- it was always going to go live with the 2012 phone.
I mean obviously if it was a disaster they would have to go back and cut another deal with Google (or Nokia/MS) but it now becomes obvious why they held back turn by turn from the old Maps app for so long. Because you can legitimately argue that 6.0 Maps with some weak spots that can be improved over time but with turn by turn plus possibly Google Maps in the App store is better then 5.0 Maps powered by Google's superior data but without turn by turn.
Wasn't the agreement renewed at the late-in-the-game last year? Is there any reason to think Google would have turned down a renewal (on the previous terms, we know there was friction over new features) this year?
I'll plead ignorance if it was up last year although just shifts the thinking above. So let's say Apple Maps was planned for 2011 but by wwdc they realized releasing in 2011 would be a huge disaster so they had to go back to google for another year.
As far as Google I'd guess they would have been fine to continue powering the default Maps app. Google's price might have gone up from 2007 but the quality increased by a similar amount.