You just completed the mission, how did they or he reappear?

Zetsu who then watched you go on a mission again without your partner.

Zetsu slightly opened the Flytrap that protects the head and torso. White Zetsu: That's right, we've been watching again, your frivolity is amazing.

Black Zetsu: We have not yet informed Pain that you will violate his decree again.