The True Master.

[Boromir88]

This is from the movie. Sauron had a physical body even without the Ring, and he was perfectly capable of surviving without it. In fact, he very nearly overthrew Middle-earth without it. Thank deus for his machina.~obloquy

Yes, I know that, I mean he wouldn't be able to survive (in a physical form) if the ring was destroyed, or if someone else mastered it. He would then remain just a shadow, never able to take form again.