Unlike many, I firmly believe <PERSON> is NOT dead physically. I will explain.
This is my theory on how <PERSON> death in the library could be avoided by an older Doctor, who has been brooding over her death since it originally occurred in the library:
In the episode Silence in The Library, <PERSON> is seen taking the Doctor's place and saving 4,022 people, enabling them to live again. This makes the incident a fixed point in time in which lives depend on the event taking place. The Doctor cannot stop this event nor take her place, because doing so would mean he never met <PERSON> & <PERSON>, they never spent their wedding night in the Tardis, and as such, Melody/River Song would never have been concieved in the time vortex and <PERSON> would never meet the doctor, nor save him and the 4,022 lives in the library computer core.
The 10th Doctor managed to save an electronic record of <PERSON> consciousness in a sonic screw driver that a later version of himself (11th?) gave her prior to her trip to the library.
There is a way to save her (physically and wholly), yet still have "her" take the Dr's place in the library. The Doctor now has a Sontaran as a part time "sidekick"﻿ (See: The Snowmen). Recall the scene in The Sontaran Strategem in which <PERSON> was cloned. She was placed in a recliner next to the <PERSON> clone pool and a perfect copy of her was created from goo, that had her memories and her ability to function in the real world without the clunkiness of something on the order of the Teselecta (Series 6).
The Sontarans have perfected cloning. This technology would allow the Doctor to put <PERSON> in the chair, creates the clone, then perhaps he takes it to the singing towers, gives it the screwdriver and <PERSON> will still live. 837
I can't imagine the Doctor knowingly sending a loved one to her death (with years of foreknowledge and planning available) if there was ANY way it could be avoided.
<PERSON> tells the 10th, prior to dying in the library, that at her last meeting with him, he had a new haircut, a new suit, took her to the singing towers of darillium, and that he cried. Perhaps those tears were shed because he made the choice to send the clone, the perfect living replica of <PERSON>, with all of her same memories, that (by his perspective from years past) was willing to die in his place. We see a glimpse of the Doctor having to make this type of tough moral choice in The Beast Below, when at one point he was faced with releasing the star whale and subjecting the humans aboard the UK spaceship to certain destruction or allowing it's torture to continue. The Doctor decides to numb the whale to the torture so that it can continue for a few years and keep the humans alive. Luckilly, <PERSON> has the Queen abdicate, turning the torture system off and they realize the whale wanted to serve the ship all along.
When it comes to keeping his sweetie alive past the Silence in the Library, the Doctor may well have to make the tough choice of sending a clone in her place. It would keep her alive and would work perfectly with no apparent plot holes. The doctor has indeed become very acustomed to clones. There was a clone of <PERSON> through her pregnancy with the Doctor, a clone of <PERSON> as a baby that <PERSON> thought was real, and of course, the Doctor himself had a ganger and a teselecta replicated him.
The facinating aspect would be that from the Library forward, <PERSON> and the Doctor would have a properly forward moving timeline. 45