Well, after going from frustrated to problem solving, I figured out that I could heat the furnace up to about 1650, which softened the flux and allowed me to pry the silver up with a screwdriver. I then grabbed on to it with a pair of long handled pliers and gently worked it out. Thankfully, the muffle refractory is still in good condition, less the flux.
I still have 10 grams of silver missing, and I'm pretty certain it's in one of the vent holes, so that will require taking this thing apart and torching it out.
i still haven't figured out the dish though. there are no cracks that I can see, so all I can figure is that there is a hole in the bottom. I haven't heated it back up yet to investigate. If that didn't happen, the flux managed to push the silver (chunks, not sponge) out of the dish.
Or, the neighborhood cat came in the garage and jumped on the furnace while I wasn't there.