My first playthrough, I removed the vallaslin. Since I self-insert, it goes without saying that my Lavellan reflects my values. I cherish freedom in many a form. Artistic freedom, personal freedom, freedom of thought and choice... Onward this list could go. It's a steady conviction for me. My Lavellan removed it because the idea of wearing something that symbolized slavery didn't sit well. Furthermore, it was also symbolic. It represented her choice to move forward, to accept that she was not the same woman she had started as. She is still her, but a her that has a new array of scars, of experiences and wisdom and knowledge, and of layers and depths. She could never return to her clan, vallaslin or no. She has changed, but more than that, she has seen too much and become too a part of the world's conflicts and struggles that to abandon it now would go against her beliefs and who she is. She may not have chosen to be Inquisitor, she may be less than unsuitable for the role in her mind, and frankly suck at it for some time, but it's her responsibility now. She can't just drop everything and go back to her old life after that. This isn't even going into her problems with the Dalish. I want to say in advance I do love them, but I cannot romanticize them or ignore their faults. These are faults that my Lavellan was privy to long before the Conclave. But now between Solas, and Mythal, and all other things she has seen, her reasons for not returning have just been added to. She loves them to death. They are her family, her friends, her people, but her love is not, cannot be wholly blind. She loves them in spite of their shortcomings, but those shortcomings are there and she cannot altogether leave them unacknowledged. I really hope this isn't interpreted as me hating the Dalish, because I don't. They fascinate me and I adore them, just as my Lavellan loves them. I just don't think it's right to completely ignore their flaws.
However, my second playthrough I stopped before the Temple of Mythal for unknown repercussion reasons. Now, though, once the Black Emporium is released I want to get her sliders and start over again, because I tweaked some things in my keep worldstate, but that is neither here nor there. I don't know what I'll do this time. It's definitely something I'll have to think on. I could go either way, personally, and know it would be true to self. On one hand, there's what I said above. On the other, this vallaslin has been part of her for years, and has taken a new meaning through her. But could she hang onto it, even if it defines something she has qualms with? Perhaps she can. Perhaps she can take this mark of slavery, wear it with knowledge of its origin and of her abhorrence for what it once meant, tell it that it no longer means what it once did and give it a new and better meaning, and accept it for that and nothing more or less. Again, I don't know what I'll end up doing. I'm more than a little conflicted, so we'll just have to see.
Edited: For adding.