Lina destroy him with little to no effort
Lina is far more powerful, and much more stronger arsenal. Voldemort will speedblitz her with his broom... if he starts out with it and Lina will just let her get speedblitzed. Also, Voldemort wont do it either, he didnt against Harry, and he wanted to kill Harry more than anything else, so what will he do with Lina. He'll get crushed like a pudding.
Not much reason to keep this open. Magic in the world of Slayers is capable of attacking both physically and astrally, meaning Voldemort's immortality wouldn't be able to help him out much here. Also, many of Lina's spells cause greater destructive capacity than what the Harry Potter-verse could muster up.
Afraid I must lock this up.