" In T2, Arnie loses his hand before being sent into the lava.

I don't think they melted it or anything. The cybernetic hand might've been it, aka "The hand of God" as that wacky professor said.

Cameron said everything must be destroyed to prevent D-day. EVERY part of the robot.

Either that or they just forgot about it.

Maybe it's a plot element, or maybe it's a plot hole.

let's debate"