Just a point of info if anyone encounters something similar.
Last night, as my daughter was schooling Rudy, the game just up and died, as if someone had unplugged it. Not a reset, just dead.
With a sudden loss of all functions, I initially assumed a fuse, but all fuses checked out after being removed for testing.
The power driver board had 3 LEDs illuminated. They were labeled "18v", "20V" and "LED 7" (12vdc). Nothing was illuminated on the MPU or any other board in the backbox. There was no indication of 5vdc anywhere on the board.
The signs seemed to indicate that this was a power-related failure, so I started investigating under that assumption. After following the 5V pathway as described on PinWiki, I eventually got to connector J101. I disconnected it and then reseated it with the intention of checking for voltages at the various test points on the power driver board. At that point, the game booted normally. Two of the pins on the J101 header were looking a little toasty, so I hit them with some DeOxit for the time being. I will be replacing header shortly. The connector had been replaced sometime in the past, and I may well replace it again, since it's not the type of connector I would have used, and I can't say for sure that it has Trifurcon pins.
I consider myself an intermediate pinball tech, and this was a pretty scary failure to experience. I write this in the hopes that someone with the same experience in the future will find this after a brief search and have something to try.