He ignores his offers for information. He was an enemy. For Kanda, Mercury was the only reason he was alive right now. He had sworn to protect her, and any way he hurt her would also mean John would take revenge on him.

It is only her word that guarantees his survival. Until she chooses otherwise.

He stays silent, his shield and blade following Kanda's head with an eerie precision. If Mercury bolted away the second the enemy freed her, that would mean there would be no reason to leave him free, let alone alive.