Given the wages and level it makes all the sense in the world to sell Higuain and go for a cheaper backup. Kean would be ideal for a role now but maybe that can't happen yet.
You won't sell Higuain for the book price no matter what. nobody will pay that much for him. Cheaper back ups might not be on his level as well.
The last thing I believe is Kean coming back to warm the bench after last Summer where he was sold for playing time. He'd also command quite high wages as for a backup, he's Raiola's client after all.
The best thing now is to negotiate with Higuain for an additional year while trying to lower his current wages per year - to spread it over two years (with some additional money thrown in of course). In that case you could offer him for example 10m net for two years, instead of 7.5m for just one. His book value would be much more digestible and we would have a valuable backup striker for the next two years. Creative accounting obviously sucks but every club plays this game nowadays.
Now go and spend those money on the midfield. CR7, Dybala, Higuain as strikers is very good, especially if you compare it to the midfield we have right now.