"First flight" is to "maiden voyage" as "final flight" is to....?
Swan song?
From Wikipedia:
The swan song is a metaphorical phrase for a final gesture, effort, or performance given just before death or retirement. The phrase refers to an ancient belief that swans sing a beautiful song in the moment just before death, having been silent (or alternatively, not so musical) during most of their lifetime. This belief, whose basis in actuality is long-debated, had become proverbial in Ancient Greece by the 3rd century BC, and was reiterated many times in later Western poetry and art.