Wow, you all are much more spiteful than DH. He's mildly annoyed by all this, but the additional stock grant was not why he stayed back in spring, and I'm not convinced he'd have any kind of legal case. He's okay with sticking around a couple months for a clean exit and some severance pay. I don't think he's going to hesitate to negotiate/demand the occasional work from home day when there's an appointment or some other need for it, but he was working mostly from the office already. If he managed to hang around another few months, it would result in 1/3 or 1/4 of a stock grant issued last spring. That's money we don't urgently need, representing an additional sliver of a company we're not too impressed with.
The business model by headquarters seems to be to buy up somewhere with a relevant-to-them technology, operate it as a subsidiary for a few years, then close it down, keeping the intellectual property but not the intellects. It's not a great strategy to declare that a technology is "done" and likely to stay that way, but that'll be HQ's problem very soon.
I will encourage him to set his post-employment contracting rate at a good, high number that will make it worth their while to find a way not to have to call him and make it worth his while to advise if they really do need it.