I always assumed that since they "became" mortals due to losing their powers, I believe all 3 perished in the abyss of the Fortress Of Solitude. In regards to Kal-El saving them, he should have, but then where would he place them? The Phantom Zone was destroyed & beings such as them were far too powerful, or rather had the potential if they were ever to regain their abilities again. In the comics & animations, Superman would never kill or destroy life, because it'd go against his moral standards, but you never know or can't be sure.