Perhaps just a disguised layoff? A percentage of workers will not come back, and in case layoffs have to happen; that percentage is already out of the picture.
At least in my country (and I guess in most of europe?) each worker pays % of salary to social benefits fund that pays unemployment benefit. There's severance pay on employer for no-fault separation though. Which is now lowered specifically to avoid situations when employers push people to „voluntarily“ leave.
Yep. You've summed up the situation 100% accurately.
Yes, however the law recognizes that creating a hostile environment to force people to quit is essentially firing them. Which means in that case you can quit, then move on to filing paperwork claiming it was due to the hostile environment, go before a government body, etc.