The speaker turns down cryonics, the practice of freezing a body in hope of revival, and says he would rather be a puddle than a Popsicle. He treats it half like a sales pitch: immortality for $29,999 (he jokes that he has the cents but not the dollars). Then he describes the process bluntly. The blood is flushed out and replaced with blue fluid, and the body is bagged and hung upside down in storage.
The humour is dry, and it covers real doubt. He wonders why future scientists would bother reviving him, and guesses it would only be to question his "pickled brain" about a time when people could not see past their own vanity. That suggests he sees the whole scheme as a form of vanity too. The ending returns to the opening line, and "evaporate" sounds calm, even content. The mood is wry and a little defiant. He would accept disappearing rather than be preserved as a curiosity.