I've had two sudden, total failures of my 2012 Macbook Air drive: once in warranty where it got replaced, once out of warranty. I have indeed been using a USB3

I've had two sudden, total failures of my 2012 Macbook Air drive: once in warranty where it got replaced, once out of warranty. I have indeed been using a USB3 external SSD drive for the OS ever since. Inconvenient, but it works quite well.