Sit in the machine with no power. What is working? The clock. Via the battery relay bypass circuit. Pressure instruments. MAP. Skid ball. Balance string.
With battery still OFF, engage the clutch switch. Power now appears to go through it via the bypass circuit, to the tachos and a pile of other stuff on the 28v bus bar.
Start the engine, then turn the alternator and battery switches off. See what is still running. That bypass circuit is still alive, until the battery is depleted.
Then you don't have a lot. Your ears will tell you if the RRPM is right. Your eyes tell if the attitude is correct. Your left hand tells you how much power you are pulling. You have been trained in governor-off operations, so your ears will tell your left wrist how much to tweak the throttle. Eyes show if you are in balance, and how far above the ground you are. Fly yourself, using known power settings and attitudes, to a hover, and put it down somewhere that an engineer can get to you with some electrical assistance. Just don't do this at night.