There aren't, and never were, any guarantees that the overtures towards North Korea would work. That isn't a reason not to try.
We have some very smart, rather hawkish guys in key foreign policy positions -- Pompeo, Bolton, Mattis, Kelly. If, after a reasonable period of time, it becomes clear that the Norks were just screwing with us all along, I have little doubt that Trump's tone and approach towards them will change significantly. As I posted elsewhere, Trump bending over backwards in this effort actually makes military action more likely, because there will be no alternatives left to try if this effort fails.
But a week isn't a reasonable period of time to make that determination.