I just had this issue for the first time. Had a bag of Cannith crafting materials I collect up from all my toons via shared bank. Nothing remotely as valuable as OP's bazillion-hours-of-play treasures. So, I search for the issue, and wind up here, reading this horror story.
I just logged my toon that lost the bag back on, and noticed that I have in-game mail. Checked the mailbox, and have a message from Lost & Found, and there's my lost bag!
Didn't see if you'd already checked the mailbox in your posts, but I've got my fingers crossed for you.