OK, so considering a situation like this: someone sends Bitcoins and doesn't include a transfer fee. What happens to those Bitcoins if the network "decides" not to deliver them to the destination address? Are they returned to the sender?
Good question. Anybody knows an answer?
They were never sent in the first place then and are still on the old address.
(might only be that some clients don't show them, because they are marked as "reserved to be sent")
Bitcoins are never "lost in cyberspace" they are always on a Bitcoin address.
That makes a lot of sense. But isn't it kind of pointless for a client to generate a transaction number for a transaction that is never going to occur? That's what's confusing me. And from what the OP said, it seems that at some point the transaction was showing on blockchain.info.
If you look in the other thread, you'll see what happened that a transaction was sent out that relied on a previous unconfirmed transaction. The second transaction was rejected and removed from the network.
The client creates a transaction number and broadcasts the transaction, so that miners can grab and include them (and blockchain can show the transaction), but until it's included in a block the Bitcoins didn't move.
So, in a nutshell: the Bitcoins were sent from an address belonging to the casino and blockchain.info showed the transaction until it was rejected by the network because of insufficient fees. That way, the Bitcoins remain in the casino's original wallet. Now it's up to the casino operators to verify that and, if they're honest, correct the OP's balance on their site or send the Bitcoins again with enough fees. Correct?