No, Sobell, didn’t roll or a take a plea. He was convicted with the Rosenbergs and served time in Alcatraz. He has only talked recently and is still alive as far as I know.
BTW—ladies and gentlemen, David Greenglass is alive as well and has admitted to saying incriminating things against his sister, Ethel Rosenberg, to protect his own wife who was much deeper involved in the conspiracy than Ethel ever was.
Then you should reserve your ire for Greenglass for incriminating an innocent person via his perjury.