Science works by evidence-driven consensus. There is no central ruling body that decides what "science" is, or how long to keep working on it. Different scientists make proposals to different institutions, and those institutions decide what to fund. As long as there are tenured researchers or funding institutions that want to work on string theory, there will be people working on string theory. But if research into string theory stops yielding interesting results, those still researching it will get fewer publications and citations and they will change to a more promising line of research.
Also, scientific theories are never "proven", and the word "theory" doesn't have any sort of officialness to it, as is clear in the Wikipedia article you linked. To be a "theory", a set of ideas basically has to be comprehensive, logically sound, agree with existing evidence, and generally useful for something.
Experiments and consensus determine which theories are most promising for continued research and experimentation. In a given domain of science, the simplest theory (see Occam's razor[0]), with the best agreement with available evidence, with the most useful predictions, and with the greatest consensus, might be considered the "accepted" theory of the day. An accepted theory can be displaced if new evidence does not match predictions made by the theory and the theory cannot adapt to the new evidence, or if a new theory provides better agreement with evidence while being simpler or more predictive.
Science as a process transcends human lifetimes. Sometimes it takes a new generation of scientists to see past the blind spots of a previous generation, but that doesn't mean that the previous generation wasn't doing "science".
Also, scientific theories are never "proven", and the word "theory" doesn't have any sort of officialness to it, as is clear in the Wikipedia article you linked. To be a "theory", a set of ideas basically has to be comprehensive, logically sound, agree with existing evidence, and generally useful for something.
Experiments and consensus determine which theories are most promising for continued research and experimentation. In a given domain of science, the simplest theory (see Occam's razor[0]), with the best agreement with available evidence, with the most useful predictions, and with the greatest consensus, might be considered the "accepted" theory of the day. An accepted theory can be displaced if new evidence does not match predictions made by the theory and the theory cannot adapt to the new evidence, or if a new theory provides better agreement with evidence while being simpler or more predictive.
Science as a process transcends human lifetimes. Sometimes it takes a new generation of scientists to see past the blind spots of a previous generation, but that doesn't mean that the previous generation wasn't doing "science".