If a single bottle of holy water were proven to cure a dying person once and never again, science would recognize that the event actually happened but would treat it as an unexplained anomaly rather than evidence that water has healing powers.
Scientific knowledge is built on patterns and repeatable results, not isolated incidents, so a one-time miracle cannot change established understanding of biology or medicine. Scientists would likely investigate possible natural explanations—rare spontaneous remission, unknown biological factors, or diagnostic errors—but the fact that it never worked again would mean it remains historically remarkable rather than scientifically actionable. In other words, science could acknowledge the event without revising its general claims about how the world works, since singular miracles fall outside the domain of predictable, testable laws.
The minimum, the only view needed, is that it is an anomaly. That is all. Science has unexplainable in mind. That does not mean supernatural. But could it allow for it? Well science still says that natural explanations - even unknown ones - are probably at work. The supernatural suggestion does not have the same weight.
Religions will say, "Science declares that it does not know. We go a step further and say it is supernatural. After all, when nobody knows, it could be supernatural. The two interpretations are correct - they just don't tell the whole story. They overlap." That is false. We have to go with what is necessary and probable and supernatural interpretations violate both.