Unless it is found unconstitutional by the US Supreme Court. Fat chance of that happening.
Not necessarily. The Missouri law does not allow for the uncontrolled carrying of concealed weapons. It does regulate who may carry and what they must first do to be allowed to carry. The consensus is that nothing in the Constitution prevents the legislature from passing laws like this. It'll go to the state Supreme Court and will probably be overruled.
If the state Supreme Court does uphold the ruling, however, then I doubt that the U.S. Supreme Court will overturn the decision.