Why not interpret it as “after all this, and if that’s the future, I’d rather leave”?

I think it’s a bit of a point of no return for both sides. Musk wanted all chips on the table, got them, and it turns out his hand isn’t as strong as he thought. There is no going back to status quo after this email stunt, it literally made clear that the majority of employees are just sticking around until they find something else, and would even leave sooner if at all pushed to. This is a sinking ship.

I have no firsthand knowledge, but from the screenshot alleged to be the email, it did look a lot like a phishing email.

This all seems plausible to me, but if this is the case doesn't it weaken Elon quite a bit going forward? If a boss at any company says "Everybody do this simple thing or you're fired", and a bunch of employees respond by rolling their eyes and walking away, that manager has to either fire a bunch of people or become a joke. Or maybe both happen, issuing an ultimatum like that is usually pretty dumb.

I can imagine that the only folks saying yes would be folks on visa and those who cannot be without health insurance or those who like working for abusive folks (there is a not insignificant number who does prefer some level of abuse in their life). For folks on visas things can get sticky rapidly without a job and they may not want to jeopardize anything until they've lined up the next job which takes a bit of time especially around holiday season.

My understanding is that laws covering mass layoffs have resulted in a plan to keep them employed normally for 2+ months (they just aren't showing up to work and don't have access to systems), and then the severance would be a lump sum after that. So I don't think Twitter would be liable to pay out 2-3 months of salary immediately, but that severance package is still going to be a big dent in the company's funds when it comes due in a couple months.