The nice thing is you can link stuff like hp and ac in the little circles on the token to the character sheet and then edit the character sheet to make it the default token. For the wild shapes, you do the same thing, but do not actually link the hp to the NPC sheet. Just type the actual values in to the token before saving it as the default token. That way, the hp is not remembered from one time you use it to the next. Then you can delete the token when they switch shapes and drag the character sheet back onto the map for the correct shape. The wild shapes start at full health, and the druid hp starts wherever it was before the wild shape.