The DSMB has the authority to end the trial for compassionate reasons as they are directly responsible for the safety of all of the patients, including the placebo patients. They can do so in order that the placebo patients can be provided with the active drug if the data is so overwhelmingly positive that it would not be humane to continue the placebo arm. This has no immediate direct bearing on the the FDA although they will undoubtedly be interested in expediting a high priority review of the trial including that data. This is very rare so don't get unreasonably hopeful, but it does happen. The FDA and the company would then move forward according to the established appropriate protocols and perhaps work together to establish new ones but the drug would not be given any kind of marketing approval without further confirmatory and statistically significant trials.