> sort of thing I’d expect from a programmer!
Well, this is still called Hacker News. Am I in the wrong place?
Anyway... you've created many strawmen here, where should I start?
> you decide to leave? Then what?
My "hiring" for it would imply defining a proper budget for it and a set of conditions negotiated a priori. It's not really "I will just do the job myself", I'm talking about "ok, you are willing to pay $80k/month to have this solved. Here are the 5 other different plans and solutions that we can implement and that will cost less than that, which one gets the go-ahead from upper management?"
> make a mistake that takes 24 hours to fix: that’s thousands of people unable to work
It's still coming out ahead of Github that took 11 days to solve?
Also, what is that joke about HackerNews overloading with traffic whenever there is a github outage? Or that one of how half of the internet GDP being tied to AWS?
Seriously though, the answer would be "you don't migrate everyone at once". You'd start with these migrations on a project-by-project basis, starting with the less critical projects on the new system and slowly weaning off on your dependency of the big vendor.
Bonus: by migrating your systems you will have some kind of redundancy. If GH goes down, the teams could use the opportunity to move to the new system. It it works, the teams gain confidence and can accelerate the migration. It it doesn't, it becomes an opportunity to learn something out of a sunk cost.
> If I had 10k people, and I could pay $50k to offload ownership of some critical infrastructure to a third party
Paying $50k is not giving you any guarantee that your business is robust. You are just paying for CYA.