I'm curious, what does everyone want when it comes to the outcome of their respective elven Inquisitor? Whether or not it's within the boundaries of the game design, is there an epilogue that you specifically want for your Dalish protagonist?
Well, in my world-state where Nasir leads a Lavellan, a Trevelyan, and an Adaar alongside him (and previous companions join the Inquisition as agents), Marisa would like to study the knowledge the Well of Sorrows granted her -- and Merrill, Velanna, Vanessa Surana, Lysa Mahariel, Morrigan, and Nasir -- to learn more about their past, as it's clear that what they remember is a tale that never was, of an era that never existed, with a people that were not as great as they thought.
She is torn between wishing to do what you suggested earlier, which is using the knowledge from the Well to create, or find, a new dimension with which the Elves could settle down in peace. While on the surface this seems a good idea, it has drawbacks. It's isolationist in nature, and worse it demands that they be unable to monitor the situation on Thedas. And if somehow the humans were to gain knowledge of the Eluvians and find them, they would be taken by surprise.
So she, at Nasir's urging, decides it might be better to take advantage of the political precedent set up in Ferelden, Wycome, Kirkwall and Orlais. With Briala's Eluvian network and her agents everywhere, coupled with Denerim's new Bann of the Alienage Shianni, and Clan Lavellan having a seat on the Wycome City Council, and the few reforms Tobias Hawke and Merrill were able to enact in Kirkwall for the Elves in the Alienage before he fled from the Red Templars shortly into his time as Viscount to begin to help the Elves.
Orzammar also counts itself as an ally of the Elves under King Xanthos' rule, though very few Elves choose to live underground I think. I dunno.
With enough time, and influence, the Elves would be better poised to do the whole "Live in another dimension/world" thing and rebuild, as they would be able to receive information from agents stationed in Thedas through Briala's chain of spies.
Risky, to be sure, because who knows what the future might bring. Some Elves down the line might distort history and then you have a war between the Elves from this other dimension invading Thedas and the Thedosians therein. Or something else bad might happen. The future is anything but clear, but I think that's where she would start.