The P0440 code indicates that the vehicle ran a leak test on the evaporative emission system (which includes the fuel tank) and it failed the self test.
Periodically when the engine is running, the computer will seal off the fuel tank and evap system by commanding the solenoids in the system closed, and then open one to allow engine vacuum to draw a vacuum on the system. It is then resealed, and the computer uses a pressure sensor mounted on the top of the fuel tank to monitor for vacuum decay. If the system cannot maintain vacuum during the test, a fault code is stored to indicate a leak is present and the light is turned on. This self test is capable of detecting pinhole leaks equivalent to a .001 inch diameter hole; it is extremely sensitive.
Since you know a fuel leak is present, that is likely why the test failed; the leak will need to be identified and repaired before the system will ever be able to maintain a vacuum. Not being able to see your car, I cannot tell you the exact point your fuel leak is coming from; you will need to drop the fuel tank and visually check to identify the leak point. Being that someone recently had the fuel pump module out to replace the pump, the most likely point that a fuel leak can occur would be at the rubber seal where the module is sealed to the top of the tank. It only takes one very tiny speck of dirt in between these parts to cause it to not seal properly...
Hope this is helpful!
The code you ahve stored is an evaporative system (emissions related) code. You will not damage anything by driving the vehicle untill the tank is almost empty before attempting repairs.
The only concern would be the fuel leak; if it is coming from teh top of the tank area it should stop leaking when the level drops slightly. If it is a leaking fuel line connection, it may continue to leak. A fuel leak is always a safety or fire hazard for obvious reasons.... you may want to monitor the leak to make sure it stops after a while before deciding when to correct the problem.