Inevitably? Strong words.
In fact, the simple parts are usually the most difficult to discover. Why? Precisely because it takes extreme genius to give simple answers to mathematical questions. Over time complicated proofs and definitions get simplified and clarified (such it was with calculus, set theory, logic, group theory, and countless other topics).
So there's no precedent to believe that current mathematics won't be simplified in the future (unless, of course, you believe that all mathematics is complicated; but then you seem to be trying to make an objective point about complexity, so we'll ignore that possibility).