Flood Damage

I accidentally drove my car (Nissan Sentra 04) through a flooded street (about 2 feet) of water at about 45 mph and it came to an abrupt stop after some rough hesitation. I tried to start the car several time with no success. I have comprehensive insurance on my vehicle so my insurance company towed the vehicle to a repair facility. Now the repair facility and my insurance adjustor are telling me that the car suffered a blown head gasket and it was because the car overheated not because of the flood. I called four different mechanic shops and all of them told me that a blown head gasket can in fact occur from this incident. They gave me a few examples to support their theory: water entering the engine through the intake can damage many parts of the engine or forced water could have damaged the radiator fan which in return overheated the car and blew the head gasket, etc. Also, the repair facility my car is at said all they did to diagnose the vehicle was removing the spark plugs (1/2 hour job). They said once they saw coolant (an ASE certified mechanic I spoke with questioned how in fact do they know it was coolant) coming from the plugs they came to their conclusion. Many ASE certified mechanics have told me that the shop my car is currently at did not diagnose my car properly and the flood could have blown my head gasket (because of many factors) and other parts in the engine (pistons, rods, etc) which can appear after a more in depth diagnosis. Please advice. Thank you in advance.