Its Danny Pink you're thinking of.
Just because he's dead doesn't really mean he's going to stay dead.
They could bring him back to life, they can have Clara travel back in time to see him again and get knocked up somewhere along the way or even
bring him back from the past as a series regular only to have a dramatic final episode where he "has to go back" knowing he's about to die.
Plenty of options really.
It's a show where writers can do whatever the heck they want as long as they come up with a good enough excuse for it.
Personally, I was hoping for a somewhat darker and more complicated Doctor.
Not to say the season was bad, but I don't think it lived up to the promise of having the doctor push his moral boundaries.
In fact, I'd have to say that Smith's Doctor was actually darker and creepier at times while Capaldi's just comes across as older and grumpier.
The Danny Pink story arch was also rather rushed and it didn't really have the dramatic effect they ware going for.
It was fun, and Nick Frost was a fun-enough Santa.
I thought that was the show's little Christmas joke (Saint Nick and Jack Frost) until I read your comment and looked it up. Having a guy actually called Nick Frost play Santa, brilliant :)