Plant closing and notice period questions - any advice?

I received a formal notice about a mass layoff at my workplace. I do not know if I should start looking now or wait for severance news. Should I stay for the bonus?

Keep everything in writing and save the confirmation numbers. It made the follow-up calls so much easier.

Thanks for writing this out. I went through something close to it 11 months ago, and it got easier once I kept a simple log of every call and form.