It won't be that everything in the car is connected on one bus. What is more likely is that you have a zonal ECU that controls a group of a few sensors and actuators. That zonal ECU will likely be connected to other parts of the vehicle through more traditional Ethernet. The 10BASE-T1S standard requires that it can support a minimum of 8 nodes on the bus although you can support more but you aren't going to be hooking up absolutely everything together on it.

>Would one single broken wire disable the entire car

Not in this case but try shorting the two CAN bus wires together in an older vehicle.