Højlund is going to be Napoli's main CF in the absence of Lukaku. His return will probably be no earlier than mid December for now.
I don't think so, in Napoli's latest match, Lukaku was not in the squad, instead of playing Højlund, Conte preferred Lorenzo Lucca as a starter. Napoli's next match is against Fiorentina & it's not impossible that he'll feature in that crucial clash. It would also be an opportunity for him to prove to Conte that he belongs at Napoli. But back to my initial thoughts, I'm not sure Højlund will play. It might take some time for Conte to get him back into the side.