Well, I'm baffled too.
I mean, I'm glad she's going back, but if it's to be to a reduced role then what does that mean, really? That she gets killed off by mid-season and/or all her scenes will be shot over a short period of time? And what will that do to the overall narrative? Because if it's too heavy on Hilltop goings-on...well. I mean, the possibilities and how it'll pan out is interesting, it's just a shame it's unlikely that the show itself will be.
Why bother teeing up the whole 'civil war'/Hilltop vs. Alexandria thing if they even thought Lauren Cohan might be/was walking away? Why not just do as they've done to other actors and make their minds up for them by killing the character (or you know, 'not quite' killing them off)?