"Earth to Earth" by Alan Moore, Rick Veitch, Alfredo Alcala, and John Totleben.
By this point, Swamp Thing had gone to Gotham City to rescue the imprisoned Abby, had a run in with Batman, got Abby freed, and then was--more or less--assassinated by Lex Luthor.
Commissioner Gordon, Batman, and other members of the GCPD attend a memorial service for the Swamp Thing, and of course rain begins to fall.
Its a quiet ceremony, but there are others who attend:
And while the Stranger is correct in saying he can find no trace of the Swamp Thing on Earth, that didn't mean he was truly dead...