When the bad guys torch one sprinkler head the entire system shouldn't go off. Each head has a fusible element so that each head can apply water only to the hot spots. The master alarm is set off by the drop in water pressure not the sprinkler head itself.
The .50 cal rifle has shot the door to the vault out. The pallet with cocaine sits right behind the door, but is unharmed.
Stella picks up a phone and states that the "landlines" are dead. The phone she picks up, and those seen in other places and on other episodes are not landline phone but IP phones. With the network/Internet down, the phone system went down with it.