RTD had wanted Matt anyway.

The actual reg in the special was crap.

Ecclestone regen made sense & so did Matts but the self sacrifice just felt a bit silly.

So as Tennant wanted to stay time was rewritten in the Whoniverse!
Im guessing from what your saying, that no regeneration would've happened at the end of End of Time, so no farewell tour, no crash landing in Amy's garden!

Also they would've had to write Day of the Doctor differently, as Tennat's Doctor would've had to have come from a point ether from between series 2 and 3 or between 3 and 4, with no queen Elizabeth I! or would they have written that bit anyway?

There would've been no Doctor Donna, Rose could've stayed in the Doctors universe not the parallel one, as there wouldn't have been a human Doctor that committed genocide!
Donna and potentially Rose could've travelled with the newly regenerated Doctor, although one or both of then could've decided that they didn't want to as he had changed!
In time of the Doctor he would've had 1 regeneration left, unless Matt had wanted to leave after doing the specials year and 2 full series?
In which case instead of the Doctor the Widow and the Wardrobe, we would've had a regeneration scene there and I'm guessing it would've been Capaldi then perhaps?
So series 7 would've started with a new Doctor not Matt and this new Doctor (which may or may not have been Capaldi), would've been the main Doctor for the 50th, but I'm sure that Matt and Tenant would've both been in the 50th still!
That would've made the 50th even more interesting with 4 Doctors for most of it and not just clips!
I think Time of the Doctor wouldn't have happened till say the end of the Doctor that started on series 7, meaning that Time of the Doctor would've been say 2015 or 2016 when that Doctor decided to leave! (I'm guessing Moffat would've stayed the extra year till that Doctor left so he could solve the regeneration limit!)

All of this might have been if there was no mettacrisis!

And thats a bad thing?

Journey's End wouldn't have been as good. As someone else has said we wouldn't have had 'Doctor/Donna'. Plus, the 'Meta Crisis' Doctor wouldn't have been around, either.

Also, Donna wouldn't have had her mind wiped of the Doctor and her Tardis adventures.

The 2009 Specials wouldn't have happened too. It would have been a completely new series with a new actor.

Catherine Tate may have decided NOT to leave. Also, Matt Smith may not have been chosen for the lead role.

Gallifrey wouldn't have been mentioned. No Timothy Dalton as Rassilon.

In effect, The Time of the Doctor would have been diffrent. The Doctor would have gone to the end of his life, with no regeneration. That would mean no Doctor Who TV series after last year.

So, we should be grateful to both RTD and SM for everything that's happened since 2008.

I didnt say one way or another just roughly how different it would be.

Im sure we would've still seen the return of the time lords and Gallifrey, it would've happened at the end of what would've been a series 5 in 2009.
Which Im sure would've featured the stories of 'Planet of the Dead' and Waters of Mars in some form or other during the 'alternative' series 5.

Series 5 that we had would've then been series 6 and so on ect.
So Series 6 (equivalent to the series 5 we had) would've been in 2010, series 7 (equivalent to the series 6 we had) would've been in 2011.
Then I think there may have been a change in actor in the 2011 Christmas episode (regen number 13).
Then in 2012 we would've had a series 8, with some things like series 7 that we had, but with a difference as we could well have had a new actor.

Then in 2013 we would most likely have had a series 9 with Day of The Doctor going ahead similar to how it did but with a different main actor/Doctor.
The Christmas episode for 2013 wouldn't have been Time of the Doctor, just a regular Christmas episode.
In 2014 we would've had series 10 being the last series with the last incarnation of the old regen cycle with Time of the Doctor being the Christmas episode of 2014.
Then from then onwards with the new cycle starting with series 11 in 2015, instead of the new cycle starting in 2014 with series 8 as we are having.

I disagree that the show would've stopped with Time of the Doctor, as its a very popular show and the BBC would want to keep it.
I think that we would've seen two actors after Tennant (if his regen happened in Stolen Earth/Journey's End) as there was another regeneration, but I can think another actor would only stay a year like Eccleston, I think they would've found someone like Matt and David that would've wanted to stay longer.

I do agree that a whole series would've been needed in 2009, as it would've been a new Doctor and that he would've done a run of 3 series (5, 6 and 7), with the first done by RTD and the second and third being done by SM.
Then Moffat would've probably wanted to do another run of 3 series (8, 9 and 10) to finish his time with a second actor.
I can see the 50th being similar to how it was, as Moffat would've wanted something big like that.

no plot line, plot twist, different actor choosing or otherwise would ever dictate the end of the show. The show would only end if the makers wanted it to end which obviously they didn't back in 2008 or indeed now. had it been needed they would have completely ignored the regeneration limit even if that's what it had taken to keep the show going. They wouldn't cancel a highly succesful show for a year's old bit of information