IS this possible to unload funds from the card and convert them back to btc and withdraw them?
There are no funds loaded onto the card. Its the IBAN account which are funded with euros when you send bitcoins to the linked btc address. When you use the card, it checks the account if it has any money on it. The card itself does not store any money.
As for reversing the bitcoins you send to Mistertango, you cant. You can however use their linked exchange to buy bitcoins but Im not sure if you can pay with the Mistertango card or if it works. I use the account for converting btc to euros.