To imagine the consequences, you have to understand what is the meaning of 'P =NP' : If P = NP, we are able to solve every 'hard problem' in a polynomial time. Thus, there is no 'hard problem' anymore. Every problem can be rewritten to a polynomial problem (easy problem) and thus, be solved in polynomial time with a polynomial algorithm.
The whole cryptography must be rethinking. And this is not a tiny think. Every protocol, every communication, every auth will be rewritten.
Do not underestimate the consequences about this.
Cheers !