A droplet is a cluster of water. It does not need to have anything else, much less a nucleus. When it evaporates, it does not need to leave anything behind. Nuclei is the plural of nucleus. So if droplets did have nuclei, the correct way to say the sentence "After the droplet evaporates, the nuclei is still there", would be "After the droplet evaporates, the nucleus is still there." You are just using nuclei everywhere to try to sound smart.
Viruses do not have nuclei, or most of the rest of the mechanisms of the cell. The best I can figure, you want to use the word virion. That is the virus particle that travels around and then infects a cell.
Masks appear to work best in reducing the viruses going out, rather than the viruses coming in. So lets say an infected person were to sneeze, cough, or even speak, droplets with the virion would come out of the mouth. These droplets are collected by the mask, or even if some get around the mask, do not travel as far due to loss of kinetic energy due to the mask.
The two questions you might want to ask is how good the mask is at stopping the droplets, and can the virion travel far without the droplets? Clearly the masks do stop at least some of the droplets, but no one knows how many, because we do not know how small of droplets the virion can travel on. While the evidence is far from conclusive, it does not seem these virion travel well without droplets.