WARN is a 60 day notice and there are a few exceptions. There are 2 that apply to Yellow.
First, is the company can avoid WARN if they are actively trying to gain capital to save the business and if issuing a WARN would damage that ability.
Second, if they're filing for bankruptcy the court can decide the terms of WARN. If they file bankruptcy before closing, they're in the clear but they can not continue to operate after filing.