For River, this occurs between The Angels Take Manhattan and Silence in the Library.
In Forest of the Dead, River tells the Doctor about her previous encounter with him. Quoting directly:
The last time I saw you – the real you, the future you, I mean – you turned up on my doorstep with a new haircut and a suit. You took me to Darillium to see the Singing Towers. What a night that was. The towers sang and you cried. You wouldn't tell me why, but I suppose you knew it was time. My time. Time to come to the Library. You even gave me your screwdriver. That should have been a clue.
All of which matches nicely with the end of this episode. So unless they visit Darillium twice, her next meeting with the Doctor is in the Library.
This is alluded to during the episode – she’s getting close to the end of her diary.
And as @tilley31 points out in the comments, when the blue alien is reading her diary, he says:
The Pandorica opens. That sounds exciting. And goodness me, a picnic at Asgard. Some people really know how to snack, eh? The crash of the Byzantium – didn’t they make a movie of that? Oh, Jim the Fish – well, we all know Jim the Fish. And you’ve just been to Manhattan.
The last line is a reference to the episode The Angels take Manhattan.
(The only Manhattan-based episode I remembered was Daleks in Manhattan, which occurs before River Song has been introduced.)
[This section was heavily revised after I slept on it for a few hours. See the edit history for the original version.]
Could we see her again? Maybe, but it would need to be a bit special.
In this episode, she believes that the Doctor is limited to the standard 13 incarnations, and isn’t aware of Peter Capaldi’s Doctor. Since she goes directly to the Library, there’s nowhere in her timeline for him (or a later Doctor) to meet her without her realising that there are more Doctors.
(They could do another episode in which, as this episode starts, River is completely unaware of who the Doctor really is, but that might be hard to pull off more than once.)
The Guardian’s review recounts Steven Moffat at last week’s BFI screening, when asked whether Alex Kingston would reprise her role as River Song. He’s keeping his options open:
I killed her off in her first adventure, I wrote her as a ghost in another adventure, I wrote some minisodes for a DVD which were definitely her last appearance. There is no way to kill off River, she started dead!