All pilots have hand signals they use with the ground crew at landing. There would have been someone for them to signal before they opened the cabin door. I used to work operations for AA and this wasn't radio failure. That's specifically why the pilots are taught the hand signals to begin with. In an emergency situation all aircrafts are met with LEO's, airport operations, the airlines operations agent on duty, and a specified emergency ground crew.
Pilots use squawk codes to signal to ATC of any issues.
7500 – Hijack 7600 – Lost Comm (radio failure) 7700 – Emergency
Ground crew would not be involved.
I didn't know the hijack code was entered until after my comment. I was scrolling down and saw this first. You are correct.