The ‘death’ of a metaphor is the loss of a connection between a metaphor and a specific word, not the loss of the conceptual metaphor itself. ‘Dead’ metaphors are words and phrases that were previously metaphoric, not conceptual metaphors that have disappeared. Conceptual metaphors generally ‘outlive’ the specific words and expressions that involve them.

Mixed metaphors with two source domains that don’t make sense together, […] are the structures that most deserve the name ‘mixed metaphors’.

...all humans are given the same set of primary-metaphor building blocks, but different language and cultural groups put the blocks together in different ways. Some individuals even force the blocks together in ways that don’t fit – which is the major reason we get mixed metaphors.

Conceptual metaphors generally ‘outlive’ the specific words and expressions that involve them.

In general, the specific words in metaphoric language are less important than the concepts that the metaphors are comparing. Critics often pay attention to metaphoric words instead of concepts, simply because words are easier to identify. It’s straightforward to decide that a metaphor includes the word like and therefore is a simile. It’s harder to pinpoint what’s wrong with lightning that pirouettes or what’s interesting about a window that resembles an eye.