IMO it would be hard to justify Iowa over Illinois if Illinois is 17-6 in conference, 1/2 game ahead of Iowa with a H2H series win at Iowa. Iowa's RPI would have to be significantly better. Lets root for Illinois to fall behind Iowa in the conference standings.
I highly doubt that 1 series will be the deciding factor. They are going to look at the teams entire body of work. Illinois has to have a strong finish to the season in order to get into at large consideration. They don't have any games remaining against opponents that will impress anyone. They cannot afford many more losses.