Whats the purpose of dual plugs? Is it redundancy or are they fired at different times?

I experienced a dead cylinder when one plug wire developed approximately 40K ohms leakage to ground. I would have thought the coil pack secondary windings to be isolated.

The "A" plug fires at the same time, every time. The "B" plug alternates firing just before, or just after the "A" plug on each compression stroke.

So why does shunting one to grnd via 40K kill both?

I'm not sure what you mean by "shunting one to ground". The suppressors have 2K ohms built-in to them. Increasing the resistance to 40K makes it impossible for the spark to jump the gap.

I'm not an engineer, but it's a safe guess that the coil design/function kills both outputs when one has excessive resistance.

Yes, 2k series resistance in the wire. But I have 40K resistance to the metal shield on one wire. There should be no current flow to the shield or ground. Otherwise, the coil is loaded and not allowing the voltage to reach the potential to jump the plug gap.
I just don't understand why they would not isolate the two plug HT circuits.
Multiple fire could be achieved with one plug if that is what the designer intended.
Redundancy would make more sense but it does not appear to work that way.