Don,
That schematic is not correct for the current version of the tacker. Several of the trigger assembly parts are not correct on that schematic. Even if you have that version of the tool you'll have to convert parts. I've attached the current schematic.
Most likely you lost either the trigger actuating spring or the trigger actuator button itself when the parts fell out.
So between the plastic orange trigger (GO-215-9) and the actual internal trigger switch (GO-115-B1)inside the tool, there is an outer spring for tension (GO-115-8), a very tiny inner spring (GO-115-6A) sits inside of that spring, and goes up into the tool to act as a cushion between the internal switch and the trigger actuator button (GO-115-10). The trigger actuator button looks like a little miniature mushroom made out of metal. The stem of that "mushroom" goes up inside the outer spring and rests against the tiny inner spring and when the trigger is pulled it pushes up and compresses the inner spring enough to push the internal switch trigger causing the tool to fire.
I'm betting you lost that inner spring (GO-115-6A) when things let go. It's a common problem. The actuator button stem isn't long enough to compress the inner switch trigger without that spring being in place, that's why it isn't firing.
I wish you were closer. I'd could fix it for you in about 2 minutes. But hope this helps. I've fixed a whole lot of these over the years.
FYI, I have parts. We're a distributor for Duofast.