Slightly off topic, and this might have been covered earlier, but I didn't see any signs in my occasional forays.
It is probably safe to assume Grayven fully charged the Orange Ring before he returned the lantern (and how is that lantern doing with Alan's Green Ring, I wonder?), so he has a backup that others will have forgotten about. You know, for that time when he really, really has no other options.
But, in that ring, unless he updated it, and he might not have, is a version of his original form's perfect state (Wholeness Rightly Assumed) from before he took the Venombuster. At least, I would assume he would keep a backup copy, in case something went truly, horrifically wrong. It seems like the thing to do. So, he does have that, if he was that smart. Which, I would assume he is. In fact, the smart play would be to update it each time he thinks he's happy with his new form, in a new save file. So, taking him out would be harder than expected, and if he REALLY had to disappear, or go undercover, well....