the residual fuel pressure in the rail normally leaks down over hours to days, but all the fuel is not going to drain away through one poorly closing injector. If that was actually happening, the oil would be diluted with fuel, would it not?
Ive pulled my fuel line and had it disconnected for HOURS. The fuel will not just leak away from an opening like that, the tank is lower and if the check valve in regulator is working the lines stay full.
Nor is the fuel pump going to completely lose prime from one dripping injector. It will only lose pressure, not its prime. Might get a little air bubble, thats about it.
a dripping injector that leaked so much fuel as to drain the lines, would have washed that cylinder and cracked the piston, and ran like a dog beforehand.