To whom it may concern: I've decided to leave for a while. I'm having one of those existential crisis dealies (as faggy and melodramatic as it may sound), and I need some time to clear my head. If you have any questions, or desire to communicate, I'd appreciate if you'd hold off until I feel ready to return. It may be a long wait. Or maybe I'll decide to come back in a week. Only God knows, but until then: Goodbye and Godspeed.

I have always found this apt for a farewell:
To absent friends, lost loves, old gods and the seasons of mists. And may each and everyone of us always give the devil his due.