Question while on the ground

During my MSN->ORD->SAT very late night trip last night I was paying more attention to the planes around me on the ground. Thanks to IF Live, I now notice things like pilots turning lights on and off when crossing runways, no strobe lights on the ground, who has the right of way, etc.

I swear the taxi at ORD took longer than the flight from MSN to ORD, but it made me wonder something as it seemed we were very close to the plane in front of us. How does a pilot know if the plane in front of them is slowing down? Does the pilot constantly have to evaluate distance or is there a screen with a little white line like what we see in our live ATC?

Bonus question - When we were at about 2,000 feet, a woman went to the restroom and the attendant did not notice. She started banging on the door and kept looking out the window. Outside of the obvious safety factor, what ramifications would happen if the landing would have occurred?