I really don't get this, River Song's character is built up so slowly during the last seasons. It took ages to begin hinting at River Songs relation to the doctor and that was great.
Now, in a single episode, Rivers whole youth, the identity of the young girl regenerating in the alley and the entire backstory of how River Song was brainwashed by "The Silence" as well as the fact that she CAN regenerate is wasted away "just" to save the Doctor because it isn't his time. Think about it, there have already been myriad instances where the Doctor survived without having to resort to regeneration. (Even "fish fingers and custard" could have provided a useful antidote for just about 200 years, right in time for the doctor to be "killed".)
Think of the potential of having a second regenerating character added to the series with the econo/technical advantage of switching actors for free is gone in a single episode.
It feels to me that someone higher up in the tree has pulled the plug on River because she cannot be allowed to become official Doctor Who canon. :( The store could have kept going for years with the Doctor getting older and her getting younger and eventually either one regenerating if absolutely necessary.