Without the Sharingan, he could do nothing but watch his team painfully be cut down and made an example of in front of the remaining shinobi population. He wanted to tear his eye away from the looks of anguish and frustration splayed across the faces of his team, of his once fresh-faced genin who didn't deserve to have their lives end like this.
As Obito swatted away the few suicidal shinobi who were desperate enough to attempt to save the last hope of their world, Madara conjured up his gunbai to, one by one and starting with Sakura, drive the weapon across their necks and behead them. It was the screams that ensued, Naruto's feral and Tsunade's broken, that caused the rest of the unwilling onlookers to rush them. All were easily dispatched, just as brutally as their best medic in the war. Sasuke was the next to be executed, his own death witnessed only by the last few shinobi.
"You must be wondering where your sensei is, Naruto-kun." Madara teased as he carelessly dropped Sasuke's head down the cliff and impassively watched Obito get rid of those shinobi. "Obito has something planned he wants to do before he kills you."
He nods at Obito to teleport them, to which the other Uchiha happily obliged.
"Sensei." Naruto breathed. "I'm so sorry. I failed."
"No, you have nothing to apologise for. I'm the one who is sorry." Kakashi sobbed, kneeling in front of his student. "I couldn't stop Obito."
As Obito kicked Naruto's back and held him down on the ground with a foot, he smirks at Kakashi and hovers his sword over the fallen Jinchuuriki's neck. Keeping eye contact, he laughs as Kakashi's unmasked face twists in horror and disbelief, and crimson splattering them both.