The Lakota, (depending on the tribe for the spelling and pronunciation), prefer not to say good bye, but rather, I'll see you soon, or "I'll see you again someday" which is spoken in an abbreviated...
Sioux
Lakota has the words mahpiya (a cloud in the sky; sky; heaven) and op'o (a cloud of steam or dust)
Lila Waste (pronounced: lee-lah-wah-shday)
Nata (pronounced: Nah-dahn)