Can a Grundfos pump fail, letting water out of a cistern?

Midday yesterday, we heard a super-loud sound of water rushing in the pipes of our little house, and upon checking, saw that the pressure tank had dropped to zero. We diagnosed a break in the water system on the well/cistern side of the main shutoff. We shut the cistern pump off at the breaker, but left the well pump breaker on so it could replenish any water dipped from the cistern for household use. The rest of yesterday was spent digging a six foot hole big enough to work in where we believed the break to be. A couple of standing pipes that allowed access to shutoff valves for the garden were full of water, so we thought the break was somewhere near there. Once we got within two feet of the pipes, the hole began to fill with water, and despite using a sump pump to keep the hole as dry as possible, water kept coming in. First from one side, then from another, giving us no idea where the leak actually was. So, we called it quits just before full dark, when the rising water caused the lower sides of the hole to fall in, covering the apparently intact pipes and fittings again. This morning, the level of the 2,500 gal cistern was down by more than 1.5 feet. That's a TREMENDOUS amount of water. The breakers for the well & cistern pumps were turned off all night, so that shouldn't have happened, right? Nothing's frozen, no heavy equipment has been within a half mile of the pipes, and this was a whole heck of a LOT of water, both all at once when we lost pressure, and then slowly overnight. Yesterday, the entire house system emptied in about 30 seconds of rushing sound. So, here's what we know: We have a nearly-six-foot-deep hole big enough to shovel in that keeps filling with water from all sides, which water erodes the sides of the hole as it comes in. We have a concrete cistern leaking significantly. I expect it'll finish today, allowing the water level to rest at the same height as the leak. (We're filling every container we can find so we're not refugees later today.) The only holes in the cistern are on the top for access and one at the bottom where the pump pushes water into the pressurized line. We're getting the sump-pumped hole water downhill and as far away from the hole & cistern as possible, because the clay backfill has deep cracks that can channel water back to the hole (which we discovered the hard way yesterday). When the breaker is on, the cistern pump powers on and sounds like its running, (you can feel the vibration of water moving in the pipe just before the main shutoff in the house 150' from the pump), but there's no resulting pressure in the system when it's on, and we can't see any evidence of where it's going from above ground. Any ideas? We're pretty dumbfounded . . . and anyone we know who could help us if off on emergencies today. :o(