I know this because ESPN said so here. That's also where I saw the following quote from Illinois head coach Ron Zook:
"I just told them they're getting ready for the Arena League," Zook said. "If they don't make it to the NFL, you go to the Arena League."I think that the fact that Ron Zook is their coach alone means they're playing Arena football when they leave. It's not the fault of Wrigley Field's right-field wall.