I say Goodbye of course. To me the word is just that -a word to say before parting, as yum-yum is a word to say before eating or good night before sleeping. Formalities, nice mannerly phrases which once meant the same thing to everyone , but now, thanks to semantic shift mean other things as well. There are many examples of this---most swear words, the words gay, nice, bloody, sophisticated---there are lots and lots of examples. A word, as Humpty Dumpty said means what you wish it to mean, and I do not ever intend to "bless" anyone or invoke the divine when I wish, for example, to say good bye, or call them a bloody nuisance.