I understand what you are saying about real life, but I don't think the analogy works.
Maybe there is a time when it would be appropriate to say goodbye. A sad and fond farewell, perhaps. I don't think it is appropriate to take shots in a farewell. I've seen that, along with the "don't bother to respond I won't be back" routine.
I've left forums, not so much explicitly as just lost interest and felt no need for fond farewells.
I know where you are coming from, because your farewell would most likely get ignored by me. ROFL.