From what I see of the market, its an employees market - "there are hundreds of people waiting to replace you" doesn't mean those people are good, experience or worth what they would replace. It's EXPESNIVE to replace an employee and the prospect of doing it for 80? 100? 500? employees is something that Tim (and his management) can't ignore.
I would tell my manager if it was just me - I wouldn't send a letter to Tim ("The CEO")... but this is a weird time and there are PLENTY of stories on HN or... well everywhere... about how many employees have a taste of WFH and are considering job hunting if the options aren't acceptable after COVID.
I do agree everyone is replaceable though... but the cost would be extensive if it comes down to it and THAT many people leave.