Sensors are not magic. They have specific, defined parameters. What you describe are automatic E-stops. There were no sensors saying there was a problem with Big Thunder Mountain Railroad.
Not knowing the cause is exactly what makes parts falling off machinery an emergency situation.
All ride systems are still manually checked because the sensors do not cover everything. It was during such checks that it was discovered that Space Mountain at Disneyland was no longer structurally sound and had to be closed immediately.
A young man died because of a runaway monorail. A portion of Monorail Silver was burnt to a crisp because it continued on its way after what most would consider a small problem, a flat tire.
Yes it was above my pay grade, all I did was drive the trains. The beam is checked daily for obstructions as part of the opening procedures. It's just one of those things where there are so many factors involved that something will eventually go wrong. Take for example tires. The load tires on the monorail are never used for the full length of miles they are rated for. The beam way due to being elevated is almost always completely free of any debris that could damage a tire. Theoretically a tire should never ever have an issue on a monorail, yet occasionally and rarely one goes flat or ironically also in the case of Monorail Blue something much worse.
There isn't some magical system that knows everything that's happening to the entire monorail system. There are sensors that give indications of an error. It's up to people to interpret those errors as well as others to interpret what they can see. If someone sees a problem they have the ability to stop things.
I can only confirm that I know of several scenarios although highly unlikely that could create a runaway monorail or disabled dangerous monorail that continues on its route unknown to all.
Only for specific scenarios that can be monitored. Even then, they could potentially override those systems.
Well the answer is really yes and no. There is a vast number of things that will cause a monorail to automatically stop. Other things require a person making a judgement call and paying attention. This is true of virtually any ride or transportation system.
They may be doing maintenance, however, based on available maintenance time, the reliability of the monorail is pretty poor.
