Unless you are on a full fare ticket, and I suspect you aren't, the airline will almost certainly cancel your reservation when you fail to present yourself in Dayton. If you do choose to show up in Chicago before your flight was scheduled to depart Dayton or to call the airline about this, they will almost certainly charge you an "add collect fee." This would represent:
1) the difference between the fare you paid to depart from Dayton and the higher fare you would have paid to depart from Chicago
2) the difference between whatever advanced purchase discount fare you bought and the lowest fare available for your flight now.
In other words, if you show up in Chicago to do this, you will probably wind up paying full fare for your trip. In the eyes of the airline, they sold you transportation between Dayton and Miami, and the stop in Chicago means nothing. Should you choose not to travel between Dayton and Miami, they have no responsibility to accommodate you.