It must be feeling great for Manchester City to find Gundogan's replacement right away. Kovacic would be a great alternative to him I think. He has been an important player for Chelsea for many years hence I don't even know why they were okay to let him go just like that. They are in a rebuild phase maybe but Kovacic shouldn't have been one of the players to be wasted easily. Thanks to this cheap transfer (29m euros) Manchester City can comfortably allocate more money for their other targets.
Gvardiol is indeed about to be Manchester City player. 100 million euros is the price Leipzig have for him. As Manchester City made their first offer as 90 million I guess he would join them soon.
There is no doubt that the player did well while in Chelsea but the truth is that, the club performance have discredit that players effort and at that any player leaving Chelsea will have low value in the transfer market.
Whether Gundogan will be missed or not, time will tell. Manchester City lets one player go that works perfectly within the team and knows the team without a doubt. They now got a new player and need to see how it works out. Saying that he won't be missed is still unknown in my opinion They won't fall apart or run into a major crisis because of selling Gundogan, but I can imagine games where some commentators would say that a Gundogan is missed. He has improved so much that I thought it would not be possible. 
