The parasitic drain from a built-in regulator is in the range of a few milliamps, and it would take a month or more to have a noticeable effect on the state of charge of a good battery. I cannot imagine how even that drain would have any influence on this situation, since the battery apparently died overnight with one cable disconnected ! A leaky diode bridge will discharge a battery quickly, but that should be apparent when the charge lead is connected to the alternator by the wire terminal making a spark as it's connected.
It sounds like there's either been some sort of mis-wiring done when the regulator was eliminated, and/or the battery has gone toes-up.
Jerry
