I started the quest, gave the guy the equipment that I needed while in the Embassy. I kept a lot of items such as my gold, my amulets, potions, etc. When I started the quest, everything from my inventory disappeared. I got everything that I gave to the bartender back from the chest. But everything that disappeared from my inventory is gone. Almost 10k in gold, the amulet of mara, and a few other important items are lost. Is there any way to get these things back?

I'm pretty sure you gave them to Delphine at the stables before you go on the carriage.

Okay. I went back and talked to her and am now on the next quest. She hasn't given me anything back though.

It's all stashed in a chest in her secret room.

check one of the chests in her room when the quest is done

Okay, I reloaded and noticed that she said "Your gear is safe in my room, as promised." Must have missed it the first time through. Thanks for the help, though.

Keep in mind there are two chests in her room. Some people think they bugged because they look in one chest, see nothing's there, then don't bother to find the other chest.