I say, and with God's help: His wiping is invalidated; because if one foot gets wet, he must wash the other, and it is not permissible to combine washing and wiping, thus his wiping is invalidated. He must remove the sock and wash the other foot if he is not in a state of ritual impurity; otherwise, he must perform ablution. This is because the contact of water with the foot is not a real nullifier, but rather the nullifier is the previous state of impurity. However, when his foot gets wet, the effect of the impurity appears on the foot. See: 'Umdat al-Ri'ayah 1: 114, and Sharh al-Wiqayah p. 114, and God knows best.