Digestive enzymes break down these complex molecules into smaller molecules the body can use. What would happen if digestive enzymes were not present?

We would not be able to digest and use energy from our food causing us to die.

Our body can only absorb food when it is present in the simpler form. We take the complex form of nutrients which is converted into simpler form by enzymes present in our body. Then these simpler forms of nutrients are absorbed by the small intestine in the body.

So if digestive enzymes will not present in the body then we will not be able to digest the polymeric complex form of nutrients present in our food like starch, proteins, fats.

Therefore if the digestive enzymes are not present we have to take a simpler form of nutrients from outside like in case of carbohydrates we have to take glucose to survive otherwise we can not survive on complex molecules without digestive enzymes.