IMF just disavowed after the Kremlin bombing, not disbanded.
at the end of parking lot fight scene, u heard dat Russian Police/special force agent saying to Ethan, "so, were not enemies then?"

And they found out it was Henrikson doing all this time..i think dat cleared the air between both US & Russia...hence
IMF came back to fully operational.. Do correct me if im mistaken

You must be wondering how come Ethan Hunt did not have a concussion after so many times hitting his head... XD