Hmm, I'm figuring that the Doctor dying by the Lake was a fixed point in time, because either the Doctor was always going to die there or he was always going to let everyone think he was going to die there. Like in season 4 when Mt Vesuvius was always going to explode, because of a choice the Doctor was always going to make. Heh, I remember the last Christmas special and all the debates about whether or not young Kazran and old Kazran could be in the same place and time without it being a paradox. I like to imagine that there's logic ;)

Oh please let there be deleted scenes on the box set! That would be brilliant :D