Leaking water pump little puddle of coolant on the floor

Hi there, I noticed one day a little puddle of coolant on the floor, checked it out and only leaked after the car was parked, not while driving. Also some smoke (steam) came out from somewhere of the radiator, just a little smoke, not a lot. I took it to a mechanic and he said that the water pump needed to be replaced as it was leaking, and the coolant splashed on the hot raditor which might cause the smoke. Now my car runs well, no noises, normal temperature gauge, normal coolant level ( only get refilled when change engine oil). I am wondering if I have to replace the water pump now. Will it cause any problems if I do not change it (since everthing is OK now)? Thanks a lot.