Sauron Vs the Ring

[Boromir88]

but he left a small part else where to become the "Great Eye".~Servant

Sauron wasn't a Great Eye with a spotlight, that is an invention by the movie. He indeed had a physical form and a physical presense, as the Ring's powers were in rapport (meaning 'bound to' Sauron). So, even if he lost it, or didn't have it, the Ring's power was still tied to Sauron. If the Ring was destroyed, as Manwe points out, Sauron would be reduced to impotence, he would have been a mere shadow, unable to form into another body. Though as long as the Ring was still around, Sauron could have a physical form (not a bodiless Eye), and he didn't need to actually have the Ring to form into another body, because the powers of the Ring were bound to him.