Why do you get the impression that we are selling Fellaini this Jan? If someone come in with a 40m offer then OK the club might be tempted, but no club will be that stupid for an average player who will be out of contract in 6 months time. If any club come in with say 10m bid, do you think we will sell? Fellaini will definitely stay for this season, whether he will leave in the summer is purely up to him, that's why the Mourinho comment.
As for replacement MF, don't tell me there is no better option than Fellaini? In another thread I argued that, assuming both Fellaini and Carrick positions will be vacant, let's go for 1 quality MF who can compete with Matic and Herrera (150K-180K), then promote 1 of the Academy player as 5th choice.