JohnB firstly, sorry fo late reply
i would like to change the POV: "If one PC fails" it is a wrong approach
One pc for live and one for backup is far more than enough even for "big shows" and moderm computer , if well configured, very rarely has issues.
Personally i run (big) shows with 18Gb banks each with a couple 2017 pc's: never replace one of them.
issue OFTEN are related to External disks or SSD's, beucase are usually the less quality tools than a full pc AND are subiect to magnetitims, dust, broke, falls etc...
again: 2 pc with LT installed and you're good to go even for large show (we lreay has such artists do that worldwide)