Board Thread:Theories and Speculation/@comment-34656247-20180602151532/@comment-31099706-20180602185939

Orochimaru did not revive on his owm though. With Genjutsu, Itachi can basically(after he catches him in genjutsu) make him kill himself with whatever he thinks he can be killed.

Ofcourse it's not as simple as one can think, hence the saying 'One does not simply kill Orochimaru', there are still many more not so simple ways to kill him, one shown by Sasuke and second by Itachi.