If we were where we were 3 years ago maybe. It makes more sense to sell him for 40M when you have so many holes to fill. But now? No thanks. We have arguably one hole and that is a top class SS.
If you sell Chiellini to fund the SS, you're just swapping one hole for the other. Strikers are SO overrated in terms of importance. They are a function of the team ultimately. They can be frozen out if your team sucks, defenders can't. A striker is the last piece you look for when you build a team. If your team can create 100% chances game in and game out, you can find someone to put them in the net. Even with our "crap" strikers we led the league in goals.
Add onto this the fact that Chiellini, himself, is of a rare breed nowadays. Not only does he play an important position like CB but he has the capability to actually rise to tremendous occasions to completely shut down top strikers. It is so, so rare to find a CB that can physically pound strikers and keep up with their dribbling in open space. You can put anyone against Chiellini and I won't be scared.
Who else can you say that about? I don't like how pundits and the general football fanbase cannot properly proportion their values of players. Guys who score goals vs. guys who stop goals. What is more rare nowadays? The defender that can match the striker 1 on 1 is extremely rare. Chiellini is worth 60M FFS.