I spent the day today replacing my engine oil, transmission fluid, transfer case fluid, and both front and rear diff fluids in my wife G35x. It was all pretty straight forward and pretty easy for the most part. Unfortunately I broke the oil pressure sending unit/sensor that is mounted close to the oil filter, while trying to loosen the front differential fill plug.

I've ordered a new one (part # 252404M40E). My question is, will I have to drain the oil before removing the broken sensor?

No you don't have to drain the oil. Removing the sensor with oil in the motor and screwing in a oil pressure gauge is how you check if the oil pump is working properly.

Perfect...Thanks!