For myself I can't emphasise enough how much of a game-changer that 2-parter PoN / RtD was. I bought them due to reception they were getting here, having found ZSG OK but that was about it.
At the time the post-Destiny Trekverse was, understandably, pretty grim. While I really liked the attention to detail in considering the sheer destructive impact of the Borg's invasion, there's a limit to how much I want of that. Unfortunately, if the success of Game of Thrones and others is anything to go by, lots of people like to wallow in that. I'm not that audience, but could well see it as a likely direction to go in. RBoE on its own would have only underlined this, but I didn't read that as a standalone, I had that pair prepped on the shelf!
The duo went and did what I had never contemplated - they flipped everything on its head. They showed a battered but recovering Federation, a belligerent but not stupidly destructive Typhon Pact, particularly the Romulans. Where another series would have used the events here to kick off a new war, the books went in entirely the opposite direction, even being able to render Kamenor's diplomatic gambit with Bacco exciting. That's quite an accomplishment right there.
In effect, while showing the effects of the Borg invasion would linger, to invoke Picard's line in Peaceable Kingdoms, they showed that the stories now and onwards would not be dominated or defined by them. It scaled back the doom 'n' gloom, didn't end the threats but opened the door to managing them.
So in conclusion, I don't think anyone would doubt there'd be a continuation of the story after RBoE, but I don't think anyone could have predicted the surprising nature of the continuation.