When attempting to decide how to defuse the bomb, folks of their purported intellect would know that the safest course would have been to remove the detonators from the C4. Happy, who is supposed to be a gifted engineer would have known this. She also would have known that the detonators have only two wires, hot and ground and she can easily clip one or both wires and that will disable the bomb. Not as dramatic, but more effective.
When the crew shows up at the bomb site to speak their mind, Cabe takes Walter away to talk to him personally, a Kino light extended from a stand-arm appears from the rubble above.
At 36.30, when Cabe is fighting Keeler at the parking lot, just after Cabe was thrown against a window, a crew member can be seen on the far left in front of a truck watching the battle.