The Dalish would need more than autonomy, which they have already; they would need land sufficient for all their numbers to gather and live in one place, and extracting that would be hellishly difficult.
Possibly. But it'll be a lot easier with people like Briala and Leliana in positions of power. The biggest hurdle here isn't getting the land, it's keeping it, and it's keeping other landholders from feeling threatened by the sudden influx of elves in their backyard (specifically, elven warriors and mages). That's when you make friends with people like Josephine who know how to appease the neighbors. Convince people that the Dalish
need the land, that them having it will benefit the previous landowners in some way. Make them feel like it was their brilliant idea all along and they're going to be less likely to turn on you later.
This is theoretically possible, though we've also never seen such a person exist.
We've had elves who identified with where they were from rather than what they are, even if they're not activists. Zevran definitely identified as Antivan before anything else. He considered that 'his own' society. A city elf Bann wants a say in how Denerim is run.
The ones who do want it back deserve a chance to get it, and the ones who don't want it could simply not use it. If spirits would no longer be forced into yearning for the living, it seems likely there would be no demons, so that problem would be removed. Of course, the casualty rates would be a problem, but that's why I want to find a way to accomplish this goal without them.
I don't think you can choose not to be a mage. Even if you try to suppress it - like Bethany - you're still going to be able to burn down buildings with your mind. I get where you're coming from, but if you're scared of magic or you hate it, I can't imagine anything worse than having it inflicted on you against your will. It doesn't sound like something that can be done on an individual basis, either, where you can ask permission.
Spirits represent concepts and feelings, so I'm sure there will still be Pride, Rage, Fear and Despair, etc. They may be less interested in possessing people if there's no Veil. But I'm sure they'll still cause havoc, since that's their essence.
It would be... interesting if the Veil could be torn down with no casualties. But if the one who put it up says the world's going to burn, I'm not sure how hopeful I am for such a prospect. We won't know until the next game comes out, anyway.