I recently broke that on my G37x took it to a mechanic the guy said i should change the whole subframe now is that so or there is something else that can be?
help please

 

Nothing else to do, your subframe is completely rotted away for some reason.

Did this car drive through the ocean? I've never seen a subframe 100% rust away like that unless it was actually submerged in salt water.

Does it have a salvage title?