No grace period. Legally, you are required to leave the country immediately.

If you are laid off today, you should submit application to change your status at the same day (F1, F2, H4, or B1/B2).

If you fail to do that and apply another H1b a couple of weeks later, it is most likely that you will be required to leave the country and get another H1b visa. It is very risky to do that.

In addition, if you stay in the US illegally more than 180 days, you will be subject to 3 years bar.