The problem is that once you have a resistance gene against a given treatment in the bacterial population, it is very unlikely to be completely eliminated, even after you stop the treatment. Unless the gene is actively harmful to the bacteria (some resistance genes are, some are not), there is little selective pressure to get rid of it [1]. It'll be hanging around in plasmids in a tiny fraction of the bacteria, but as soon as you cycle back to that treatment again, the resistant strain will quickly emerge again because they don't have to re-evolve the gene.
You can do the math to calculate, based on the population size, rate of reproduction, rate of mutation, etc., the chance that a gene will still exist in the population after X years when there is negligible selection on it. I don't know how it works out for bacterial pathogens.
[1] Of course there is always the slight selective pressure against anything that enlarges the genome but has no function, since it takes energy to replicate that DNA and/or synthesize that useless protein. But that alone is unlikely to purge the gene from the entire population.
You can do the math to calculate, based on the population size, rate of reproduction, rate of mutation, etc., the chance that a gene will still exist in the population after X years when there is negligible selection on it. I don't know how it works out for bacterial pathogens.
[1] Of course there is always the slight selective pressure against anything that enlarges the genome but has no function, since it takes energy to replicate that DNA and/or synthesize that useless protein. But that alone is unlikely to purge the gene from the entire population.