Unless you are completely unaware of
pop culture, you probably know the timeless
Vulcan Phrase "
live long and prosper". Created by
Gene Roddenberry, it is an embodiment of Vulcan ideals, as well as a fairly cool and dignified way of saying
goodbye.
However, this phrase seems to be part of the whole Vulcan gig, making it inaccessible to humans. So, in order to properly say ‘so long’ to a Vulcan properly, a non-Vulcan should say "peace and long life", accompanied by that "V" Vulcan hand-sign.