That's not accurate.
Hooks are made from high carbon steels and heat treated (sometimes referred to as spring steels). While it's true that a finer gauge wire or hook is more prone to straightening (obviously), elasticity (or Youngs Modulus of elasticity to be precise) is a physical characteristic of steel - there is no 'may' about it. A hook is essentially a spring - it is critical that it can flex during the fight (this is known as elastic deformation), otherwise it would just snap because it would be too brittle to deal with the loads applied to the steel. However, it's not possible for the hook to flex to the point of straightening without the yield strength of the steel being exceeded. The yield strength is the point at which the steel deforms under load permanently (this is known as plastic deformation).
So yes, a hook flexes (to a point) but no, a hook cannot straighten and then spring back into shape. The physical properties of spring steel do not allow it.
If a hook straightens, you know about it.