An H1B is valid for up to 6 years, and as far as I know the thing that changed is how hard it is to get a visa in the first place, anyone already hired would be unaffected. Tech companies spend so much on legal fees for hiring foreign workers, they're a bit reluctant to get rid of them immediately. It's also really shitty for the workers if they get laid off, since their visa is tied to employment, and it only gives them like a month to find a new job sponsor or leave the country.