By the sound of things it appeared like some insurgents were still alive and kicking outside of the building, fighting the two men on top of the roof. They were certainly persistent, he had to give them credit for that. 

...and so was the man at the top of the ladder trying to make things difficult for him. He'd have fun killing him for all of the stuff he was pulling. Rez was very strong so managed to stay on and make decent progress despite any setbacks, slowly but steadily making his way to his target. As the grenade went down and he heard his opponents scamper off across the roof, carrying out the plan they were loudly discussing a moment ago. At this point his slow and steady progress turned into a mad climb up the remaining rungs of the ladder, almost lunging upwards to take it two rungs at a time with his robotic legs, pulling himself up and over the ledge just as the explosion went off below him, making it look like another movie scene with his second close call of the night. Only problem was...he dropped his freaking' pistol during all of that chaos! His poor companion was likely blown to smithereens so was not even worth checking on after this was all said and done.

This also left him unarmed at the moment besides the fire that had now enveloped his upper body, signifying it was ready for use. He held out his hands and sent it blasting off like a flamethrower, across the gap in the building to target the two men. This would either take them out or force them to scramble away, allowing him time to get a better defense going or maybe even press the attack.