Ishant Sharma should be shown the door only if someone can enter from the opposite direction.
In a perfect scenario, ZK, PK and Yadav should comprise the first choice pace attack. However this attack is likely to never play together given the injury history of the first two names, and the rawness of the last name.
Given the other pace bowlers tried in the past two years (Sreesanth, Mithun, Vinay Kumar, Munaf Patel, Aaron, Unadkat and RP Singh), I don't think India quite have the luxury to be dropping Sharma. This represents a tough situation for Sharma as he is unlikely to play County Cricket other than a short-term stint, and returning to Indian domestic cricket is unlikely to improve his bowling as has always been handy in home conditions.
This would make a good question in however many months it is before India play Test cricket again, given we know who is available and the outcome of any potential surgery for Sharma.