However Hal Jordan hadn't snapped Sinestro's Neck. Rather he had snapped the neck of a artifical construct created by Sinestro's ally, Parallax. Sinestro lived!
Sinestro reappeared years later when the Parallax posession of Jordan was exposed. In a brutal battle with the newly freed Jordan, Sinestro was pulled back into the anti-matter universe as a result of a rupture in space. Jordan's ring confirmed that Sinestro lived.
What Sinestro did during all those years is not known, but one thing we do know.. he'll be back. And badder then before.