Mr DeSoto decided that this was great punishment for Matt, or soon to be, Keri. However, he figured Matt would probably try to get the wand back once he became Keri, so he made one final wish before wishing himself back.
''I wish this body cannot, and will never be able to walk, no matter what.''
He felt himself fall to the ground, he tried to stand up, he fell, he tried to stand up by holding the wall, he fell. He felt immense satisfaction in knowing he would never be bothered by Matt again.
''I wish I was back in my original body, and that the wand will follow me, leaving the person in my original body, in this one''
Mr DeSoto was back in his body, very happy with how that went, leaving a extremely confused Matt, or now Keri, to deal with the consequences of her actions.