Did your crayfish lose a limb?

Not to worry, most lost limbs will grow back over the next couple of molts. As long as serious internal damage was not done when the limb was lost (i.e. a lot of tissue did not come out when the limb was lost), your crayfish will be good as new soon enough.

How long is soon enough?

Well, a clean break at a joint's base will take 2 to 3 successive molts. A break that was not at the joint's base will need to be thrown off at the next molt before the process of re-growing can begin. And it will take 3 to 4 molts for the limb to grow back in this scenario.

Information from: crayfishmates.com