Nobody
Original story material is the property of the fanfic author; other material of Rowling et al. falls under the usual disclaimer.
Quirrell and the symbiotic face of his overlord lay in ashes on the staircase. Voldemort's anguished spectre cried out from the ascending smoke. "I have lost my host! My physical form is gone!"
Harry was barely able to mutter a few last taunting words before losing consciousness.
"You should have quit ......
"while you were a ......
"head."