We know she's not coming back, because pretty much everyone involved with the books has said so. I know that doesn't neccissarily mean it is definitely true (they could be lieing, I guess) but at this point it's all we have to go by.
They're not lying. If there were indeed plans afoot to bring Janeway back, in whatever form, we would have gotten cryptic non-answers (I call them 'kradswers') to questions about Janeway's fate rather than "She dead. Dead, I tell you! DEAD!"
Come to think of it, I wonder if that might not have been a better approach. It would have left fans of the character with at least the crumb of hope that Before Dishonor's epilogue despondently flicked their way, even if it was something there were no current plans to follow-up on. Confirming that she was intended to be dead as the dodo kills any suspense or mystery about Janeway's ultimate fate. Then again, I hate false hope.
Fictitiously yours, Trent Roman