Plant closing and notice period questions - 6 weeks in

I received a formal notice about a mass layoff at my workplace. I have read a lot of threads here and could not find my exact situation. I do not know if I should start looking now or wait for severance news. Should I stay for the bonus?

Thanks for writing this out. I went through something close to it 9 months ago, and it settled down once I kept a simple log of every call and form.