First of all, there's no way that Spalletti will let Perisic go. Secondly, we have only one winger in the squad who can deliver at the highest levels, although very inconsistent, and that's Perisic himself. We're selling him to include the other players, and there won't be enough room to sign and include a new winger on his level. We'll be left with out-of-place Eder, Karamoh (if he's even included), and of course no one other than fucking Candreva.
Besides, what can we get for Perisic this summer? 40m at best? Still not worth sacrificing him given the above results. We'll need more big sales and the only ones who'll do it are Icardi and Skriniar. They both have more adequate replacements in Martinez (not guaranteed) and De Vrij. Perisic has no one so he's the least replaceable out of our big stars.