There are barrier tolls and ramp tolls in Illinois.
The barrier tolls used to be just a system of manned and automated booths, but now they all have Open Road Tolling in the main line of the highway and a mix of slower electronic tolling and cash lanes set to the side of the main flow of traffic. The cash lanes at the barrier tolls are manned.
The ramp tolls are a mix of electronic tolling and cash lanes. I'm not sure if any of the ramp tolls are manned any more. Some are completely unattended having electronic tolling only.
As InterestedBystander said, if you blow a toll, you can pay it online. You have 7 days to do so. Follow the link in his post and go to the section on unpaid tolls.
My recommendation: If you know you'll be able to pay the tolls within 7 days of the first missed toll, then just use the I-PASS lanes and deal with it afterwards.