Can we survive on

No, we cannot survive only on raw, leafy vegetables/ grass because we cannot get all the nutrients like proteins, fats, vitamins, carbohydrates from them. Moreover, grass is rich in cellulose which is a type of carbohydrate that humans are not able to digest due to the absence of rumen.

We must have to ingest nutrients rich food for growth, maintenance and multiplication. So, only green leafy vegetables will not solve the purpose.