Well the funny thing is...
... River Song is not "dead".
I've wondered about this for a long time, actually. River Song is alive, digitally - her preserved mindstate, in the Library's computer core. Along with the minds of her research team, in a virtual reality.
The Doctor has known her ending all along, but also known it's not truly an ending. He COULD have gone back to the Library planet now that's safe (or should be safe?). And had a conversation with River any time he liked. We might assume that the Doctor hasn't done that even off-screen because he wouldn't want to risk accidentally learning more about his future from Digital River.
Going by that logic, I think the power of the episodes is not diminished; in fact they're more poignant in my view because it feels like a great, big, other shoe waiting to drop. We might reason that the Doctor is waiting until his forward motion through time catches up to River departing on her trip to the Library where she "dies". After that point, the Doctor should be free and clear. He knows everything that happened with River to the end of her life. Thus he would be free to at last return to the Library and contact Digital River. This is the Whovere y'know - there must be an infinite number of ways to provide River with a physical form for her consciousness to be downloaded into. (Why couldn't she just operate a remote body made of the Flesh?)
Technically, River is also now immortal. Her actress notwithstanding, within the fiction the Doctor should be free to meet up with River again and move forward synchronized in time. If she is given a new body, it could easily be as immortal or replaceable as the Doctor's.