I spent several years working for a very large semiconductor company selling to the automotive industry (memory/RAM/EEPROM, uControllers, etc.). Those customers ALWAYS required a second and sometimes third source for their major parts. If it was proprietary, they negotiated for rights to make it in their own fab, if they had one, or have it sourced or produced at an alternate fab facility. Their ability to execute and/or have enough capacity to do so was always on them though. Their JIT dock to stock (no inventory) supply chain shuts them down after 1 day of lost supply or delay, so it's a risk they manage all the time.