If the clotrimzole does not kill the organisms, will the infection return or eventually flare up again?

More complicated. Yeast infections are caused by our body's own yeast. Yeast are a normal part of the vagina and you can't get rid of it completely. The level of yeast is kept in check by the presence of a good bacteria, called lactobacilus. Things that kill this good bacteria allow the yeast to overgrow and cause symptoms. You cannot take anything to get the levels of the lactobacilus back to normal.
Yes. If there is a flare up after appropriate treatment, then contact your doctor to try another type of medication.