Mantis died? DidnÂ´t knew it. Thought in the crossing Mantis was a Space Phantom, then she (the real Mantis) was with her son in the celestial quest, kissing the Vision and isnÂ´t she with the guardians of the galaxy now?
Ah, Avengers Forever and The Crossing. One's a wretched, convoluted history-breaking debacle, that came out of the time period that was the nadir of the franchise, and has had terrible effects on too many characters, and the other's The Crossing.
Anyways, in Guardians of the Galaxy, Mantis encountered Kang, and they acknowledged the "history" between them, coming across as an ex-lover she was still on good terms with. It's the closest thing we've gotten so far to anyone making the effort to overturn all that Space Phantom balls.
As for Celestial Quest, in those History of the Avengers backups, Vision goes out of his way to deny anything ever happened between him and Mantis. Either he's lying, or that part of the story's been quietly thrown out (and if so, I endorse and support that).