There is something that could force us to sell Quag this January - money.
Lots of IFs need to become a reality in order for such a sale to happen. The first is a very good offer to arrive. Papers speculate with a 14m eur demanding price. At this point of the season, Roma could very well offer such an amount. Maybe Inter too. In the summer, when there will be more options on the market, less teams will show interest for Quag and probably none will offer more than 10m. Especially if we buy a striker and it becomes obvious that we want to sell Quag. His price will fall even more.
So, if we plan to buy a top striker in the summer, if Quag isn't in Conte's plans as one of the first 3 choices for the CF spot and if an offer ~13-14m eur comes this January, Quag could leave the team in the following weeks.
Chances are bigger that he'll stay with us, imo.