Disagree. Why make the HR team go through 900 individual calls? At the same time this will leak and other employees will learn that they might get fired before they get their own call. Recipe for disaster. Just rip off the band aid.
I believe a good approach would be to have those first line leaders (who actually have that relationship built with their subordinates) break the bad news and then the CEO speak to everybody and own the decision.
Surely after seeing your relationship status change on Facebook, they would understand?
What if the whole chains are axed? Recursive "or the next manager" could easily lead to exactly what happened: a CEO lucky to have a pandemic voiding all expectations to do something like that in person.
The entire reason companies have hierarchical power structures (in theory) at least, is so that information can be passed along with the log of the company size.
Having every manager have 10 min call with each direct report, or in the worse case a team meeting, would be much more human and could accomplish the task of notification in roughly the same time window as an all hands firing.