A weak or inoperative pre-pump would cause the main pump to work extra. Your acceleration would drop off and the idle may be affected. If you drain the tank dry you may not get started. Starting would be no problem as long as your main pump and oneway valve are ok the fuel filter is clean and the fuel pressure regulator diaphram isn't leaking. In fact if you're not an aggressive driver and don't want to blast off from every stop light then you may not see any difference in performance at all. The best way to check as mentioned is to put a pressure gauge between the main pump and the tank. Or you can remove the access cover in the trunk (non wagons) and connect twelve volts directly to the pump and if it's quiet you should hear/feel it turn on.