Umm graves are enabled so your stuff was safe in a grave
Oh well. Already deleted it. LOL My problem was that I stupidly had every last bit of food on me when I died - 16 cooked pork chops (I had only played for less than one real day). When I respawned after dying, my food bar was empty which was rather shocking to me since it was completely full when I died. Okay, no matter, starving to death with hearts disappearing, I ran down the 40 flights of stairs to the Abandoned Mineshaft because my absolute priority HAD TO BE to get to that food supply. Naturally when I got there, the cave spider was still there and killed me again. That's when I ragequit. I never even saw a gravestone because I never had time to look. But you have explained sufficiently why I did not see items scattered all over the floor like I expected.
Well, that quarry finished. No emeralds. Seems like it would require some really bad luck to not find any at all in a 64x64 Extreme Hills quarry. That makes it rarer than Draconium.
They are definitely not rare, I settled down in Extreme Hills biome (like I always prefer to do if possible) and as I built my staircase down to bedrock from the top of my mountain abode (okay, technically it was just a boring cave LOL), I gathered at least 5 emeralds while digging down. I'd say you weren't actually in Extreme Hills. Are you using Biomes O'Plenty? That's what I was using, and my Extreme Hills wasn't so "extreme", it was rather small and the majority of the land area was actually called "Highlands" biome. I always press F3 and take a look at the biome to determine the limits of the emerald ores.
All of it is within Extreme Hills biomes.
If you are 100% certain of that, then we have a real mystery on our hands here.
What biomes option did you select at world startup? vanilla, BOP, or what?