And which ones are those? Knowing what did and did not work is an actual challenge by itself.
> You need a cache, you can get one from any number of cloud providers or spin up something off the shelf you run yourself. Same with databases, CDNs, large scale object storage, search infrastructure, message brokers, and all the rest. So, yes, there might be a need for changing some of that necessitated by some key people disappearing but it's not a massive technical challenge.
The massive technical challenge is migrating existing infrastructure to something off the shelf, then finding and fixing the new bugs in that existing infrastructure and/or your deployment/configuration. That shouldn't be underestimated.