It has happened in the recent past (2-4 years ago?); I can't remember both the acquirer and the hollowed-out startup, and searches are returning chaff, but it got to the HN frontpage.
IANAL, but at-will employment cuts both ways- thr best an employer can do on behalf of investors, are golden handcuffs - and people can be bought out of those.
That’s not quite actually true and it is a bit more nuanced than that. For example, while non-competes and non-solicits are unenforceable in CA for employment agreements, they absolutely are enforceable for mergers and acquisitions.
The laws governing employment are a subset of the laws governing M&A.