Yay! I'm no longer broke.

The bank located the deposit slip they lost so the money will be credited to my account tonight. It's a relief. It wasn't as though they could just lose my money and never give it back, but it's very nice that they handled this with a minimum of hassle. They were apologetic and helpful. I guess the take home message is always save your transaction receipts, at least until you confirm that your statement is correct. Errors do occur.