At this point, I think coalitions have shifted too much + demographic changes and generational turnover have upended traditional R pathways in IL to such an extent that I don’t see how any Republican can recreate Rauner's map (not just in terms of the margins, but also the county wins themselves). It’s hard to conceive such a scenario now, but the next Republican to win IL will probably break at least 35% in Cook but still lose DuPage and Lake narrowly (and likely two other counties or so as well — Rock Island and Champaign?). Chicago would likely need to lose population at a faster rate than it currently is for this to happen, though.
In a hypothetical where the Dem wins by one vote statewide, I still think DuPage votes Republican. Lake and Champaign would be within a few points but they would vote D.
