I, unfortunately, have not had the time to read any of the novels. I'm running entirely on what is mentioned in the sourcebooks and the Wiki. I'm pretty sure Aina isn't coming back, but I can see her fighting side by side with Dunkie on the bridge.
Back in the Clutch of Dragons, there were a couple of off-hand comments that she might not be completely gone and may have become... something else.
While his activities are varied, (Harlequin) is rather focused on the Watergate Incident and the fallout, especially in regards to what happened to Aina. He is beginning to suspect that she may be something beside dead, but he is not yet clear on what that might be. He very much wants to know, though.
His anger blinds him, Ghostwalker thought. He doesn’t realize that she isn’t really gone. He won’t listen to reason, any more than I would.
I hope we'll have some answers eventually. Maybe in a third Harlequin campaign? That would be great.
Aina actually makes a brief appearance in two of the stories I'm working on, Heart of Gold and Trickster's Folly. In Hear of Gold she frees Maisie (my OC) from the astral cocoon Vestrial trapped her in, and works as an astral messenger to help them both find each other and get back to the physical plane. (She disguises herself because she feels that seeing her in that moment would be too painful for him, so Harlequin never knows it's her).
In Trickster's Folly, Harlequin is forced to confront Vestrial on his home metaplane and gets his pasty immortal backside kicked. Aina finally shows herself to him and heals him, along with some cryptic comment about how he hasn't yet reached the end of his path before vanishing again.
Basically she serves as a sort of guardian spirit, and becomes a constant thorn in the side of horrors, horror constructs, and twisted spirits everywhere. She dishes out some well-deserved vengeance on those who tormented her for MILLENNIA.