Well since a couple of people are, much to my surprise, interested in the headcanons I have for my Wardens, Hawkes and Shepards, heres a headcanon I have with my main warden, Syn Mahariel.
There is this conversation you can have with Merrill in Dragon Age 2 where she mentions having seen Mahariel but finding it impossible, since, afterall, the Warden Commander is currently missing. My headcanon with this is that Merrill DID see her. I believe Syn came to Kirkwall looking for Morrigan, wanting answers to questions that Morrigan didn’t answer when they last spoke.
However she does not approach Merrill or the other Dalish Elves in the area. Nor does she seek out Anders, even knowing he is there. After her arrival though, she takes a break from her search for Morrigan after seeing the state Kirkwall is in with the mages and templars, and observes things from a distance. She does help Hawke, discreetly, against her battle with Meredith but quickly disappears after the battle. The only one that knows of Syn’s prescence in Kirkwall, is Zevran, because he is the only one she shows herself too. It is a brief visit, sadly, because of her search for Morrigan and his situation with the Crows.