I also had this happen to me earlier this month. Both my screens froze up driving home from work. I rebooted them and only the dash poped up. The MCU was completely dead. The dash showed kph units (my preference) but displayed speed in MPG. Odometer was gone, no ability to control anything on the side panels of the dash. Or open my charge port (i know how to manually open it) the correct way. I don't know if I could charge or not, didn't need to try thankfully.
I checked fuses, and tried rebooting before calling Tesla.
This was very concerning because I couldn't change HVAC, sunroof, or really any settings without the screen. Tesla wanted me to wait 3 weeks to get a service appointment a lot farther away, but I eventually got one the following day (over an hour on the phone with service to get this appointment).
They told me my MCU was dead, I ended up buying a new one. And they told me my old part was "restricted" and I couldn't have it back. After calling them 3-4 times they agreed to let me have it back. And promised 3 times it would be in the car. Wife picked up the car, didn't check for the MCU (they told her it was in the trunk). The next day I had to drive 100 miles round trip to pick up my dead MCU.
My car was build Dec 2012, MCU screen was replaced for bubbles in 2016, bubbles started in 2015, under warranty (took about 6 trips before they decided to fix the bubble issue gratis).
This is a huge worry of mine. I was almost stuck with a borderline usable car for 3+ weeks becasue Tesla didn't think my MCU dying was critical. Not only that spending $3k becasue of Tesla burning out Flash memory over 5.5 years, is stupid to replace a $3k MCU. Pretty cheesed off that Tesla basically put a death timer of 4-6 years on this $3000 part.
Hopefully I can repair my old MCU to have a spare part in another 4 years or so when this one burns up.