A lot of Fans are panicking about the fact that following established canon - the Doctor only has two regenerations left.
What everyone seems to be forgetting, is what Lady Peinforte aluded to in Silver Nemisis.
Lady Peinforte claims to be the only one to know the Doctor's true identity. When Ace says she knows the Doctor is a Time Lord, Peinforte shakes her head conspiratorially.
Neither this nor any further televised story elaborates, although in a deleted scene from Remembrance of the Daleks, the Doctor claims to be "far more than just another Time Lord"; further omissions from Survival would have featured the Master challenging the Doctor's identification as a Time Lord.
These elements are all part of what a lot of fans have dubbed the Cartmel Masterplan.
In the Cartmel Masterplan, Susan Foreman was the granddaughter of the mysterious Gallifreyan founder known only as "the Other," a being who MAY have been reincarnated as the Doctor (due to the series cancellation it was never played out).
The Doctor had traveled back to the dawn of Time Lord civilization and rescued Susan, who recognised him as her grandfather. The Doctor did not initially recognise her, but knew that this was somehow true.
This version of Susan's origins is reflected in many other Doctor Who spin-offs.
The Other was first mentioned in the novelisation of Remembrance of the Daleks by Ben Aaronovitch as a shadowy figure in Time Lord history, one of the founding Triumvirate of Time Lord society after the overthrow of the cult of the Pythia that had, until then, dominated Gallifrey. The other two members of the Triumvirate were Rassilon and Omega.
Of the three, the Other's origins are the most obscure, with the circumstances of his birth and appearance being a mystery. Like Rassilon, various contradictory legends surround the Other, some hinting that he had powers surpassing that of Rassilon or Omega, and some even suggesting that he was not born on the Time Lords' home world of Gallifrey (which links with the Doctor being half-human on his Mothers side - as stated in the Doctor Who TV Movie).
Even his name is lost to time, which is why he is simply referred to as "the Other".
If anyone is interested, a minor Gallifreyan festival known as Otherstide used to be celebrated yearly in his honour.
If the Doctor is indeed "more than just another Time Lord" and his history and abilities go back to the Dark Times of Gallifrey, the Time Lords were restricted to 12 Regenerations by Rasilon - so the 'old ones' Rasilon, Omega, and the Other would be able to regenerate indefinitely.
Also, there are other factors to consider such as in The Brain of Morbius story we see (during the mind duel game with Morbious) that there had been additional incarnations of the Doctor prior to Hartnell. How could this be, unless there is more to the Doctor than meets the eye . . . . .
We also know for a fact that a new Cycle of Regenerations can be bestowed upon an individual (its mentioned in the Five Doctors) and that the Time Lords even had the technology to raise the dead (they bought the Master back to fight in the Time War).
Don't lose hope, Time and Time Lords will find a way.