Well, in the likely chance that the Beeb don't break the 13 lives rule, there is always that famous last line of the 4th Doctor in Logopolis to bring some closure to the series as a whole:
"It's the end, but the moment has been prepared for."
Then again, Steven Moffat is a clever sort of writer so if there is a way to bend the 13 lives rule and still have it keep to the continuity in way, he'll find it.
