After re-watching Lazarus last night I'm pretty sure they intend to keep the real Lex Luthor alive. When Clark is in purgatory he saw the "real" original Lex. Right before the lightning bolt struck Clark and sent him back it struck Lex and sent him back. I'm assuming they were both on their death bed and they were both brought back somehow. The Lex that was in Purgatory was sent back. that wasn't a Lex clone. The real Lex Luthor is alive NOW. Clark saw him and even saw him leave the purgatory. Clark should realize that. Come on...
"I'm not sure, the lex that was killed 2 yrs ago was a clone. And in the purgatory state, Lex had returned to the world of living just as Clark did. Lex's body was not at cadmus, but the regenerative clone were left there. The same person who brought Tess to cadmus is likely the same person who has revived lex. And that is presumably granny. I really don't think that boy is Lex, just a distraction. If he grows, then old Lex's soul or brain is likely to be place in the vessel"