What happens if my wallet gets "hacked" and my BTC is stolen? What if my wallet gets hacked and the hacker transfers all BTC to his account?
Is there is any way to get it back, or to open a dispute to specific address or anything else?
All BTC transfers are final. If a hacker moved your BTC elsewhere, you can't get it back.

You have to keep your funds safe. See https://en.bitcoin.it/wiki/Securing_your_wallet.