Well, in the movie, it's quite evident (consistent with the novel) that Michael presents a Corleone family that is just a shadow of its former self. That was his objective. He accomplished it. Tessio figured that he was going to get wiped out along with the rest of Corleone hieracrchy. It was a smart move; Clemenza bought into Michael's Potemkin Village ("Let us recruit some new men."). Clemenza was willing to go down with the ship.