If Clara hadn't intervened this would have been the Fall of the 11th Doctor. The Silence didn't want the Doctor to live to open the door and let the GH undo all of the Doctor's victories and leave the Universe in ruin. It was better to kill him early than to have his previous battles undone.
No no no.
If the Doctor had fallen here then it would have been a paradox because he would have fallen before he was supposed to have fallen. This is his future where he "fell in battle". The silence might be referring to that event. I don't see the Tardis falling out of the sky as being more significant than his actual death fall in battle.
Sure, but the GH going back in time and defeating/killing the Doctor over and over in the past created a paradox as well, since if the Doctor died at Adrozani, the Dalek Asylum, or in Victorian England (or all three and then some) then he could never have died at Trenzalore, leaving behind the means for the GH to go back and kill him.
"Canon is only important to certain people because they have to cling to their knowledge of the minutiae. Open your mind! Be a Star Trek fan and open your mind and say, 'Where does Star Trek want to take me now'." - Leonard Nimoy