You can get that coin. You will get mail by Jepetto Joybuzz, the Toymaker:
Jepetto Joybuzz - NPC - World of Warcraft
After you fish all the coins, go talk to him in Dalaran. There should be an option to ask him for a replacement for "losing" your coin.
That is what I did after I got the coin master. The coin is kind of useless, through.