I guess my game currently has like Schrodinger's BBEG. When I started the campaign I envisioned one, and never fleshed him out because I figured I'd have some time to do so. We're several sessions in however, and he hasn't been introduced, and I don't really think the party is on track to meet him any time soon. They met the faction he controls, but they were presented as innocuous pilgrims at the time. So he exists on paper, but I could throw him away without any major wrinkles in my game.
The issue is that my players are really great.. I set them up to chase a Macguffin (Or collection of Macguffins) and they just said "Sure", and went for it, without really questioning it.. So I haven't found a way to inject the story in.. I was kind of hoping they'd go and try and seek out information or something. I was really expecting to have to sell them on the mission.. In hindsight when I played as a teen, I was probably just a jerk making the DM have to make the quest worth my character's while before I'd bite the hook, and I expected something similar.
With that said, they've run into a different faction, and they are now kind of at odds with them. I was expecting this faction to be the stepping stone bad guys, between the PCs and the BBEG, but now I've been thinking about instead having not one central BBEG, but rather several factions at play, all chasing after the same relics. The PCs will eventually find that they are in possession of some very powerful items and some very powerful people want these items. I hope to eventually make the real BBEG the tough choice they will have to make at the end of the campaign. Once they collect all the dragon balls PowerGems will they turn them over to an allied NPC who maybe they only kind of trust? Will they use them for themselves? Will they seek to destroy them? Who knows.