The question

I work for a large national retail company. Over a week ago I was called into my GM’s office and was told that my position has been eliminated. That I would receive severance. I received an email outlining such, and my last day. That day came and I was escorted out of the building. Only withiin less than a days time to be called back. And given the option of resigning with no severance or returning in the same position, assuming my schedule. Is this legal?