He absolutely would have. Pat Quinn lost this for being Pat Quinn. A generic D (which Daley very much is) wins against Rauner.
Why was Quinn disliked so much? He has a proven progressive record. Medicare expansion, gay marriage, environemental protection, minimum wage, increased eduction funding and he even cut spending. And last but not least, he handled the situation after Blogo's impeachment pretty well.
I heard that Quinn had a difficult relationship with State Legislators (of his own party). Might that be a reason? Or the economy? California for example, another deep blue state, has economical difficulties as well, but Brown handily won.