TCS covers a wide variety of topics including algorithms, data structures, computational complexity, parallel and distributed computation, probabilistic computation, quantum computation, automata theory, information theory, cryptography, program semantics and verification, machine learning, computational biology, computational economics, computational geometry, and computational number theory and algebra. Work in this field is often distinguished by its emphasis on mathematical technique and rigor.
1) If P = NP and and the bounding polynomial is immensely huge, it would be somewhat disappointing, but interesting nonetheless.
2) if P = NP and there is efficient algorithm, it would be amazing. There are problems harder that NP-complete problems.
3) P != NP, then nothing would change.