lost all my stuff

Lag/void/shading/etc from 1.1.0 update brought me to the forums to post my concerns a couple days ago.

Yesterday evening, I loaded the game, and instead of spawning in the redstone mansion basement where I had my mega base, I spawned in the woods with zero equipment! Wandered around to restock (got back to iron weapons/armor and a bunch of maps to figure out where I was). After a couple hours of walking around, I finally found an ocean next to a dark clay landmass with a underwater monument/temple exactly where I knew it would be and knew exactly the path to get back to the red mansion.

Turns out, the 'naked and afraid' initial spawn point was EXACTLY where I should have respawned in my mega base, and ALL THE WORK that I have done in the game has been wiped completely (walls/rails/tunneling/mega base build/underwater temple scavenging and mining/totems/enchanted armor and weapons/farms/etc) have all been wiped/reset.

I confirmed it was the right location based on also travelling to a near by village that I knew was there, and finding it exactly where it was supposed to be (minus all the changes I made to it after I found it way back when) I back tracked again and found the exact topography/location of where the red mansion used to be, except the mansion is 100% gone, and it's now just a big lake with the same surroundings (mountain up from it, open field just next to the mountain, etc).

Yet, somehow with this apparent 'fix' wiping all my stuff to get rid of the lag/voids, my file size is still up around 500MB??? Shouldn't that mean my stuff is still in that save file somewhere?

I haven't gone in and changed from Survival to Adventure or Creative, I haven't changed map seed (not even sure how to), nothing to have caused this myself. One day I play, save and quit with all my stuff and builds, the next day I load up and it's as if I might as well have never played at all.