Farewell, I`ll be back in a sec?
One is used for "goodbye" of indefinite duration, the other when you are popping out on a quick errand. You kinda have to take your pick.
but anyway,
Sayonara, itterashai!
Edit -- and for the banner you got there, may I humbly suggest あさだち?
heh.
<Marcher Lord> Dogs! Oh god, please give us DOGS! There are those who press on with the ardor of beer, and those who are faint with thirst.
You can praise them, disagree with them, quote them, disbelieve them, glorify or vilify them. About the only thing you can't do is ignore them.
And while some may see them as the crazy ones, we see genius.