Plot hole: Since in this episode the Doctor is assumed to have died some time after the Runaway Bride but not before Voyage of the Damned, he was not able to prevent the spaceship Titanic from crashing in London. It is later shown that the south east was obliterated from the explosion. This falls far short of what the Doctor mentioned in Voyage of the Damned wherein he frantically repeated that if the Titanic crashed, the core would annihilate 6 billion people on the planet (that's the entire human race at the time of the show's airing).
Plot hole: In the episode, because the Doctor was not around as he was killed in the alternate reality, all the present day invasions that he stopped in the normal reality happened. However, since his death was before many invasions in later seasons in the normal reality that were chronologically before his death (for example, The Carrionite invasion in 1599) the Earth should be already destroyed. Therefore, he couldn't die on Earth, so it would be a paradox that would erase his timeline.