The self-adjusting slack adjusters are supposed to take care of that, but if they quit working, and the pistons go out without pushing the shoes into the drums; then the piston in the MC will bottom out. When that happens, with NO air in the MC , and with a properly functioning front brake system,then the pedal will get very low, but the front brakes will still work normally.
In fact, I have seen many cars come into the shop functioning this way, and the only complaint was the low pedal.
IDK about the discard measurement. I'd guess maybe .090. But the max ID is written on the drum somewhere. or should be. However, if you machine the drums, you really need to get your new shoes sized to fit them, else the shoes will;
1) initially, only contact in a very small area, the areas growing larger with time, unless
2) they overheat and glaze up, and possible crack. and
3) the self adjusters will have to work overtime trying to keep up with the rapid wear during the extended break-in period.
D) but if the self-adjusters quit, then your pedal is gonna rapidly stop closer and closer to the floor,
