Runway incursions should not happen but they ocasionally do. Pilots watch for them and react accordingly so even if it happens they take appropriate actions to prevent a problem. We had a Lear Jet landing where crossing runway traffic was instructed to go around and didn't. We ended up cockeyed on the runway using max braking when I yelled at my buddy stop this MF now and he did and held short. A Lear Jet can stop in 2,500ft by the way.
Pilots can usually figure a way to get out of a bad situation so give them some credit when things are going to hell. If there is a way out they will find it if they know what they are doing.
If you just go by the rules hoping everybody else is doing what they should and not protecting yourself, you are in trouble.