Even if Itachi succeeds, Kabuto will come out alive.
Remember, killing the caster doesn't cancel Edo Tensei. It can only be cancelled if the necessary seals are formed.
When Itachi forces Kabuto to perform the seals, by whatever means necessary, he would only have cancelled Edo Tensei, destroying himself during said action. Kabuto won't die.
He can't kill Kabuto before he forces him to perform the seals, otherwise Edo Tensei won't be cancelled. And, when he somehow forces Kabuto to form the seals, Itachi, himself, will disappear.
So logically, Itachi can't kill Kabuto.
I believe it's a great plot device, so that Kabuto can be seen later on in the series again, as another boss villain, this time as the main one.