Firing with an empty pan happened to me. After several failures to fire, I knapped the flint, pointed the barrel down range and pulled the trigger to watch for sparks. Plenty of sparks and the gun fired.
You should try it, but suggest doing outside with barrel pointed in a safe direction.
If there's no powder in the pan, the lag time can be considerable. In my case, it was like slow motion. I watched the orange glow of the sparks rolling around in the pan and I saw a couple of grains of powder, Hmm. Then a larger orange glow began to grow, getting bigger and bigger. Then I felt the recoil starting to push back and I heard the blast of firing in the background. Yes, a gun can be fired without a pan charged. Its not something to rely on however based on the number of pan flashes I have experienced. I have even had cases where the flint sparked and didn't ignite the powder in the pan. The next attempt set the charge off. I did make sure the pan powder (4f) was spread evenly over the pan.
Years ago we did a test to see how often a loaded Flintlock with an empty pan would fire. 10 of us loaded a blank charge and then stood in a straight line, muzzles up. On the command fire we all pulled the trigger. One gun went off which surprised the heck out of all of us. So we did it again. Another gun went off. After a number of tries we came to the conclusion that a loaded flintlock without priming in the pan will go off about once in 10 tries.I don't agree with you DBrevit.
I've saw a flintlock fire with an empty pan last year. No one was more surprised than me, well, maybe the owner was. Good thing it was pointed down range.
It just takes one spark to find the touch hole, and that's what happened.