Of course badges stop working when you're let go. What possible good can come of leaving the badges on? All it takes is one in 12000 disgruntled ex-employees to make it not worth it.
I'm not convinced that announcing them in advance is actually better anyways. We have partner teams in Europe who get to spend a month or more after the announcement worrying about whether or not they still have a job. Morale on the teams in the US took a noticeable hit, but the teams in EU have seemed utterly miserable for the last week.
I think it’s better to have some warning, but it would have been great if they could have said “your job ends in three months, here are your options” instead of leaving people hanging while they figured out the details on the corporate side. Or even, if paranoid about disgruntled employees, to say “welcome to your garden leave, here are your options.”