The floor for being Chicago's second team is basically the ceiling for being the first team in Nashville, Jacksonville, Charlotte, Cincinnati, hell even Indianapolis. There will be a clamor to get into Soldier Field if the Bears vacate it, especially with the city actively pimping the site to anyone in the league willing to listen.
If the Bears move its a matter of when, not if, someone comes in to take their place. Los Angeles gives zero fucks about pro football yet the NFL found two teams to move in there in quick succession. Chicago is the next largest market in the country after LA and football obsessed, it's a no-brainer.