I don't really see much upside in letting him go in January. We need another option at 9 right now and I don't see us getting anyone useful in January. If he has a useful few months for us it'd be easier to shift him in the summer.
Also, if he has a good few months for us, I could see it serving as a useful guide to the sort of player this team needs at 9, even if he isn't the long term solution, sort of like the way Jorginho signposted the need for Zubimendi; a left side biased, creative, hard working forward who knits our play together and brings out the best in our LW and balances out the right side bias.