2002 Toyota Corolla Heat shield that was loose was removed,

There was a large rattlling noise.
Mechanic said Heat Shield was loose on the Catalytic Convertor, so he removed it, and said it is not needed.
Is there a chance of a fire when park on the grass?
Is it a good idea, to have a heat shiled replaced, or must I have a whole new Catalytic Convertor replaced?