Originally Posted by ShootyDogThing:
“They're hardly going to stop such a successful series because of a vague comment made in an 80s story (sorry if that's not what you're referring to!), they'll either ignore it or work a story around it. But if you're just asking in general, then no, it won't be the last.”
I'm not sure what vague comment you're referring to but the 5th Doctor story "Mawdryn Undead" had the Doctor's regeneration cycle as a major plotline. Here is some of the dialogue:
MAWDRYN: Give us the energy of a Time Lord! Help us to die!
DOCTOR: I can't!
MAWDRYN: For pity's sake.
TEGAN: Doctor, why can't you help them?
DOCTOR: Don't you understand? If I did, it would be the end of me as a Time Lord.
TEGAN: What do you mean?
DOCTOR: I can only regenerate twelve times. I have already done so four times.
TEGAN: So?
DOCTOR: Don't you see? Eight of them, eight of me.
TEGAN: They want your remaining regenerations?
DOCTOR: It's the only way to end their mutation.