So I wonder how they're going to find him an extra 12 lives, I suspect something to do with going back into his own timestream he'll somehow come out before the 1st doctor and get all his lives back.
River gave him all her regenerations in Let's Kill Hitler. We have no idea how many he has left. Let's Kill Hitler was a terrible
episode, but that was a very smart move by Moffat, as it allowed future producers to avoid that issue unless they wanted to directly deal with it.
I saw that more as River giving up her remaining regenerative energy (and thus any future regenerations) to resuscitate the Doctor, not giving him actual regenerations.
As for Smith leaving at the end of the year, it's a bummer. Weird thing is it doesn't seem as though he's been around for almost 4 years already. He still seems like the new guy. I was like, What? Regenerating already??
Though his performances as the Doctor could be way too manic at times, overall I will miss him.