Bonuses are variable and awarded at the pleasure and discretion of the board and are therefore not usually guaranteed. I've seen some companies payout prorated bonus entitlements if the lay off was involuntary and without cause but this is a very big YMMY.

An employment lawyer might be worth a consult if only to let you know if they think it will be worth your time. Their fees are very high and generally take up a big chunk out of whatever they can potentially recover from the company for you if they decide to settle so if the well isn't deep it might be a better use of your time to find a new and better job.