Yeah, it'd go back to normal relatively quickly. Sperm quality and amount respond quickly to environmental changes. You'll father very healthy kids when the time comes, I'm sure. One way you can help guarantee this is by choosing a clean-living potential mother of your kids who'll stay away from potentially harmful substances before and during the pregnancy--and afterwards too, if she's going to breast feed. Might as well be safe since it's a relatively short amount of time in comparison to an entire lifetime.