Beneficiary passes before you do

If the person you were going to leave things to in your Will passes before you then they just drop out of the Will as they are clearly no longer available to benefit. If the Will is written correctly then there will be somebody who replaces them as a beneficiary. Typically, if you leave something to your son and he passes,  the gift will pass to his children who may well be named in the Will. If the Will is written before your children have had children then commonly the phrase issue or remoter issue is used to describe children or grandchildren that are not yet born.