What I find odd is the idea that Madigan is the only one who can draw a strong gerrymander and this weird implication that, if he leaves, the entire rest of the party will just fold and draw a fair map or something.
Madigan has a lot of influence and strength, but he's not some god. Most of the redistricting decisions are made between the members of his caucus discussing who they want to take out, what areas they want to represent, what areas they don't want to have in their districts anymore, etc. Its not Madigan just handing out decrees from Mt. Olympus on who gets to go where, its a group discussion that leads to a group decision.
No of course the rest of the party will still draw a big gerrymander but if you don't think some of these progressive or even moderate suburbanite legislators are against gerrymandering ( see virginia amendment 1) that's foolish.