In the US (and many countries) we don’t actually have work contracts as full-time employees. Offer letters aren’t contracts, as an lawyer will remind us.
Companies can, and will, change employment terms and compensation as they want.
Tesla does have an exception process for remote work, though.
Any kind of competent HR department will be able to manage a paper trail sufficient to dismiss at-will employees in a bullet-proof way, especially in a general business turndown.
A well-executed termination of at-will employees because of a change to the business environment is basically never going to fit into any of the exception categories to at-will, again assuming a competent HR department. Pretending otherwise doesn't help anyone.