I've seen, for example, how phone companies do business with one another and it's terrifyingly bad and incredibly fragile.
I can personally name a human being who is a single point of failure for half a dozen or more of the largest telcos in the world.
They would continue to exist without him, most of them don't even know *he* exists, but if he was hit by a bus they'd all have an incredibly bad few weeks/months/years, financially if not also mechanically/practically.