If D&D didn't exist, two things would for sure be certain:
1) I'd be many thousands of dollars wealthier.
2) I'd feel an aching and unexplainable void in the depths of my being.
Oh, and:
3) I'd probably play Ars Magica, Talislanta, Pendragon, Everway, Savage Worlds, or some other game with a fantasy feel, perhaps with a dash of sf thrown in. And thus:
4) I'd be just as poor, and
5) The void would be filled with the joyous clatter of dice and inspired imagination.