Goodbyes are the hardest part I suppose. The tension comes from my theory that 95% of all goodbyes consist of one person who is wringing every last drop from their contact with the other, while the other person is, while invariably sympathetic, is distractedly wondering when his plane is going to board, what his new apartment is going to look like, what his co-workers will be like.
It is an intrinsically sad affair, even minus the farewell. The sadness lies in the lack of drama. There's no tragedy in the unrequited need for feeling. Of course, there's the rare occasion that both are equally hesitant to separate. This is indeed tragic, but most times arrangements can be made to facilitate this problem.
For instance, Dylan's 'Spanish Boots of Spanish Leather' is not tragic, just really really sad. The situation is only sad for the person being left. The girl gets to go to Spain and be happy.
How to say goodbye, in light of this? I don't know. My instinct says to act preemptorily. Take care of it early. No satisfaction can come from our original scenario. Especially for the person who wants to wring every last drop of meaning from the goodbye. However, human nature and life and love demand that we try, even against all odds. My suggestion is to leave without ceremony. The people who really really love you will surprise you. Those that don't will soon be gone.