Clubs should always be preparing for at least the next season. We should have transfer targets identified for every window, anticipate who might be leaving and how we can replace them, and gradually introduce young players as and when we can.
If you don't, you end up in the situation where one sumer you have 14 players leave and have to start from scratch.
It's no different in that respect from other buisnesses with 3 and 5 year plans.