No longer existing is spoken of as melting and disappearing. Alternate translation: "Let the wicked vanish like a snail that melts and no longer exists" (See: [[rc://en/ta/man/translate/figs-simile]])
Not existing is spoken of as being like a baby that is born dead. Alternate translation: "like a baby who is born too early too live and see the sunlight" or "like a baby that was born dead" (See: [[rc://en/ta/man/translate/figs-simile]])