You are assuming that other costs apart from salaries are negligible and that firing 80% of the staff will have negligible effect on revenue.

They are pretty big assumptions to make.

First assumption, other costs are negligible: no, I'm not. Every dollar spent on salary is a dollar that doesn't go to profit.

Second assumption: letting 80% of staff go won't hurt. For that, I simply have to describe what I've heard from friends / coworkers / scuttlebutt about working at yahoo. But there are a lot of eng doing maybe a couple hours of work per day.

from

https://finance.yahoo.com/quote/YHOO/financials?p=YHOO

under opex it looks like there's plenty of fat to cut.

By that logic, businesses would never employ people because it's a cost that doesn't go to profit.

And the fat on that OPEX you linked is the writeoff from the Tumblr purchase.

For companies where employees add little/no value (yahoo!), then yes.