Any valuation of Emi by the club, whether it be £60m or £100m will be to warn off any potential suiters. The club have no reason to sell, and the player is on a long contract.
Unless Emi hands in a transfer request, the club can request £100m. He might not be worth that, but clubs either pay it or be told to piss off.
Grealish was worth about £50m max, his release clause was inserted as it was thought nobody would pay it, they did, and the rest is History.