Ok. Well now you can pop the distributor cap off for a look at the module. I don't really know of any other ways to test it beyond what you've already done. The coil is good but you're not getting spark at the plugs. The only other items in play at that point are the cap, rotor, plug wires, and spark plugs themselves. Even if one spark plug was dead, that wouldn't prevent the engine from starting and running well enough that you might not even realize you were down a cylinder. I've seen a 304 running with three dead spark plugs before. Not well by any means, but it was running. So, you see where I'm headed with this line of thinking. I suspect the module has failed either because it was a faulty product or because of an operator accident.
I've heard it mentioned that these units will display some type of discoloration if the failure was due to overheating caused by leaving the key on for too long with the engine not running as a clue for the manufacturer in case of a warranty claim. Do you see anything that looks visibly off with it? You May actually have to remove it from the distributor and look at the underside.
This is a sour development for sure. Especially since I was one of the folks advising you to go with the pertronix. Thousands of people have upgraded their ignition systems with these devices, and most I'd wager are still quite happy with them. Otherwise, it stands to reason that the company would be out of business by now. I have read elsewhere of some issues in the past with early pertronix failures such as this. The later or latest version supposedly has an override feature that is designed to prevent damage if the key is left on for too long non-running. I don't know if this is true or not. Its a shame that pertronix would still readily sell a product that can be so easily ruined by accident, if that is what has happened in your case.
Without seeing the instructions or packaging myself, I can't speak to whether or not there is some big, bold warning in print about not leaving the key on for too long. If there isn't one, there sure as hell should be. That said, leaving the key on without the engine running is not a good idea except while doing very quick electrical tests. That's why I harped on you time and again whenever I asked you to perform a test with the key on, to do it quickly and shut the key back off. This goes for pretty much all ignition systems across the board from old school breaker points, to gold boxes, to points eliminator modules. I understand that no one is born with this knowledge and sometimes it takes a painful lesson to bring it home. Accidents happen very easily too, even when a vehicle owner knows better than to leave the key on. Sometimes their friends, spouses, or kids don't have that knowledge.