In a way it reminds me a bit of my own job : the only way to avoid shit to happen is to raise as many barriers against it as possible and to never, ever, be lazy about correcting one of them when they are not up. In your case, you got 2 problems at the same time, which are both unexpected, especially together : a laptop fail + the backup laptop not being up and running because your mate didn't have time yet to copy yours onto his. For some reason, which sounds improbable but is actually theorized, there is a rule that basically says "when shit can happen, it WILL happen" you just don't know which one !
I really liked the idea of having everything available through internet, internet is everywhere these days and say having a .zip package with the essentials ready to download from anywhere can save your ass I guess. I liked the "4) Have a second laptop on stage that is up and running and actually connected to the DI boxes in case the first one fails" because I'm not sure a lot of semi-pro to pro bands actually do that and it does make sense to have the backup operational itself to make a fail-safe setup which can be running in about 5 realistic minutes