Or, for a glib answer: if you need to stop the car safely, engage autopilot and unbuckle your seatbelt. The car will turn the hazards on and pull over on its own.
Calling the critical ui interface the 'infotainment' system for a tesla is slightly misleading.
It is directly connected to the 'backend' below and doesn't go through the infotainment system/UI.
You can manually kick off a reboot of the infotainment system on a Tesla while you are waiting at a traffic light, and still drive like usual just fine if the light goes green a second after. The only non-functional stuff will be the visuals on the screen and anything infotainment related (like playing music). All driving aspects are preserved even with the infotainment system being broken/in the middle of a reboot.
ZAP!!!
(Now playing: "I wear my sunglasses at night.")
Doesn't sound that reassuring, though. For a self-driving car it wouldn't matter, but as long as a human driver is in control, the infotainment system does affect motion of the car, by proxy of the driver. Could the infotainment system, or the wipers, make a driver crash their car? I find it highly likely. Imagine speeding down the highway - suddenly, your in-car speakers start blasting your ears with 80dB music, while the wipers start to dance and the car keeps spraying the cleaning fluid all over your windshield.