I understand that prevention is better than cure but sometimes the game gets a little late and when I'm in this situation it's very hard to counter as Protoss. The picture below almost makes his ground troops invincible as if he typed *power overwhelming*.

![Screenshot of a massed group of Marines, Marauders, and Medivacs; one of the Medivacs is healing a Marine](https://i.stack.imgur.com/NFxo7.jpg)

How do you usually counter this?

Edit: Thanks to all of you, I am able to finally counter it using mass Zealot + Colossi :