Not quite. Often an evolutionary change may come at a cost to fitness under circumstances that differ from the current environment. As such, once the antibioti

Not quite. Often an evolutionary change may come at a cost to fitness under circumstances that differ from the current environment. As such, once the antibiotics are stopped, non-resistant bacteria may be better able to compete for resources and multiply. There's a reason super resistant strains are most commonly found in hospital and health care settings: https://www.cdc.gov/drugresistance/biggest-threats.html https://www.cdc.gov/drugresistance/biggest-threats.html If the ongoing cost of the mutation was truly free, one would expect it to spread out beyond these places more prominently. Edit: I may have under-emphasized that there is no guarantee, and we shouldn't rely on this property.