Revelation 20:14, “This is the second death--the lake of fire,” is a metaphor. The law of the metaphor insists that both nouns on either side of the verb “to be” are literal. Thus, both the lake of fire and the second death are literal. This is neither my opinion nor my theory, this is a law of language.

Furthermore, whenever a pronoun—in this case “this”—is substituted for a noun—in this case “lake of fire”—the pronoun agrees in gender, not with the thing to which it rightly belongs—in this case “lake of fire”—but rather with the thing to which it is being compared—in this case, “the second death.”

For those who care for laws of language, this settles it.