There was more to the story than this.
Chicago State was about to get whacked hard for NCAA violations in multiple sports, and there were probably a lot of discussions about this behind the scenes (among the other 7 conference member schools).
IPFW, North Dakota State, and South Dakota State were all lined up as expansion candidates, so if Chicago State left (and the Summit [referred to as the Mid-Continent Conference at that time] were temporarily down to 7), they were in position to expand to 10 with these three schools in short order (which they did).
I'm fairly certain that no AD / President would voluntarily take their school independent, but it was arrranged that the Press Release would state this (without explanation) to allow the Chicago State administration to "save face".
I have to believe the other schools were about to use the NCAA violations as a reason to boot Chicago State out.
Totally right Tute, I was at IUPUI at the time and the Mid-Con caught ChiState with some serious violations, especially in Women's Hoops (unfortunately I can't find anything online from those reports). There was never anything on record as to the Mid-Con schools talking about the possibility of removing them from the conference, but as you said, I'm sure there was discussions. At the time Chicago State made the announcement, there wasn't any discussion over the Dakota States as a replacement. This was caused by Valparaiso leaving for the Horizon, which left the MCC (now Summit) at 7 schools, prompting them to look at expanding. Looking back, I'm sure IUPUI was against IPFW joining, otherwise they would have been there already to even the league out. Also, as the Great West FB league was administered by the Summit at the time, had the Dakota States been an option at that point, the league might have stipulated that they stayed in there for football, as adding the Dakotas would eventually make that a 7-league team able to earn an autobid into the I-AA tournament.
What I'm not sure of is how Chicago State avoided NCAA sanctions, which does lead me to believe it was Mid-Con officials who investigated the program... however that's speculation on my part, I just know that they were in some serious trouble which caused them to go independent.