Is there a way, that I can know that my unconfirmed transaction return back to the sender?
The sender can try to start the wallet with -rescan option to check the blockchain for missing transactions.
If you were expecting coins, you can do the same to be sure and also check the blockexplorer for the txid.
In any case and whatever you do, make sure you have a working backup of your wallet.dat before you start!HTH
No, the problem is, the sender sent me coins and after he recover his wallet those coin goes back, so I never receive them. But he denied. I am sure this went back. So I want to know is there a way I can prove that the coin goes back to his wallet?
You can reindex your local blockchain with -txindex. If you are you are sure you are on the right chain and fully synched and the transaction in question is not there (fedoracoind gettransaction ) it can IMO be safely assumed that the transaction did not happen and the coins are still in possession of the sender.
The above is just the method to check for the transaction locally without trusting a block explorer, naturally you can check that on a blockexplorer too.
Mind you, there is one exception: If the coins that were sent were mined also on/during the fork, they would dissappear the same as the transaction and indeed not reappear in the senders wallet - because they would have dissapeared anyway when the longer chain took over.
But it all boils down to the senders willingness to resend the coins... Wish you good luck with that.