[Of course. He's failed them, and he cannot be left to think otherwise. If Chara hadn't said it, Mettaton would have believed them untruthful anyway. Chara must always tell him the uncomfortable truths and berate him for tasks left to pot.

Dying? That's your his fault, isn't it?

Mettaton doesn't--can't--move his head much to look at them. Such a movement requires more energy than he can expend, and with the magic that makes him up reduced to a weak, faltering spark, he really can't bring himself to overtax himself. He knows what's coming. Now, at this point? It's just a matter of when and how he will go. This time, it won't be a body failing from blunt trauma and the tick down of HP.

No, this time the HP will simply cease to exist. And then he'll shatter into a billion infinitesimal pieces, gathering into a small, useless pile of powder.]

Let's not be disingenuous. Or would you have imposed such a request on me even if you didn't think it was an eventuality? I can't really believe that of you, honey.

[They had known. They wouldn't waste time beseeching him not to die if they didn't know. Not even he's worth that much effort, or so he believes. He does oft undervalue their relationship with both Asriel and Frisk.]