It could be as simple as Garrett mentoring her for a few months, and then she goes off on her own. He will periodically check up on her, or request her help, but that's as far as it goes
Most importantly, how would you keep Garrett as the main character, and not just the mentor figure for someone we wouldn't care about as much (the girl)? How would you keep her on the side, but not completely irrelevant? What would be the main threat in the post-Keeper world?
Of course you can come up with anything you like, to me Garrett *is* Thief, and any other character becoming the main protagonist would be immediately much less interesting, so that's why him being relegated to just a mentor figure is not what I would like to see.
It could be as simple as Garrett mentoring her for a few months, and then she goes off on her own. He will periodically check up on her, or request her help, but that's as far as it goes
i would offer to be a consultant on storyline for a post thief 3,i know the story very well, and have a lot of possible idea's for a direction
and yes dewdrop will be part of the story
i feel pagan magic should be the thing used and not alter the ending of thief 3,maybe have murlocks involved as they were they most recent addition in game lore with so much not known about them, they had magic also, so no need to rely on keeper gylphs in post thief 3 it would just be altering the story when not needed
I would find it difficult to continue after Thief 3. If I was creative director of a new Thief game, I'd probably retcon to the ending of Thief 2. After all, the last lines were along the idea that "All this...it was written? And there's more?" As much as I wanted to know more about the Keepers, the group we saw in Thief 3 felt less like a force seeking balance and more like a group of people who enjoyed feeling superior and controlling things as they wished. All that comes down to Gamal poisoning the direction of the Order though.
Open world between missions sounds cool in theory, but it took away too much of the mystery of the City. The episodic nature of the first games is fine and helps keep the variety of the mission settings without creating a crazy looking city layout to accommodate.
As for a plot, it would be interesting to try and build on the idea of Garrett being a thief by having the Keepers assigning him to reassert balance in the City by moving wealth from the rich to the poor - through stealing and reassigning ownership of deeds/companies, though discovering and exposing corruption, by leaking company information to the public so they negotiate better with employers, by breaking monopolies. Parallel to that, Keepers would be interested in keeping a moral balance to society and want to reinvigorate the Hammerite Order to revive the stability they brought, leading to missions dealing with helping them retake the Old Quarter and establish charities (even if the resulting mission is just to rob blind the mansion of a wealthy detractor to fund a new Hammerite soup kitchen).