If a spiteful ex-employer wants to scrub ex-employee authorship from the entire commit history in their public repos when someone leaves I don't think there's a

If a spiteful ex-employer wants to scrub ex-employee authorship from the entire commit history in their public repos when someone leaves I don't think there's anything you could do to stop that either way, though it seems like it would be more trouble than it's worth and likely wouldn't scale. If they don't do that, assuming your old company email address still has your name in it I don't see why you'd lose credit for the work you did.