Plant closing and notice period questions - 18 weeks in

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

Write down key dates and keep copies of the notice. Mine helped when a question came up later.

I stayed for the retention bonus and looked for work on the side. It cushioned the gap.