It depends on what you mean by function. I did an internship at Coca-Cola in Brazil a decade ago. They had ~500 employees country-wide, mainly marketing and operation strategy folks. The production of the actual beverages and other products was in great part delegated to partner bottlers. My boss there used to joke that if all the 500 employees were fired at once, the amount of Coca-Cola cans and bottles sold wouldn't drop at all for months. And I do believe he was right. In the long-run, of course, things would be different - that's where marketing and strategy pays off.
There's an old joke -- "how many people work in this company -- about half"
It's probably true. Certainly feels that way sometimes. The problem is how do you determine the right half to get rid of, at scale, without getting rid of the wrong people.
Function for how long? That's the entire issue.
If everyone at Facebook stopped doing everything they do, it would continue running for a good long time. The content quality would decline. Big advertisers who need individually tailored relationships would leave, but expenses are low enough that would not kill it. The EU would impose fines for hateful content, but failing to pay would take a long time to adjudicate.
The same effects happen in failed LBOs all the time. Big companies crash slowly, and their ghosts linger.