Atleti should probably be able to cope missing 2 transfer windows, their squad is filled with quality youth. Oblak, Gimenez, Lucas, Saul, Koke, Carrasco, Griezmann, Vietto (if he returns) are only going to get better over the next 12-18 months.
Real is a strange one though, not sure on the idea of them relying on Casemiro over the next season and a half.