Transactions are kept in a wallet file along with the private keys for addresses. Your wallet.dat simply stored it for a very long time. As I assume you want the coins and want that transaction to go through, you could rebroadcast it and if the fee isn't high enough, use the CPFP method to get it confirmed.

You should go to Help->Debug Window->Console and type , that should give you the hex that you can push to any online service like this one https://blockexplorer.com/tx/send.