The bond and the caskets are connected in several ways. First, they both involve a form of risk or chance. In the case of the bond, Antonio is taking a risk by borrowing money from Shylock, knowing that if he fails to repay the debt, he could lose his life. In the case of the caskets, the suitors are taking a risk by choosing a casket, not knowing what message it contains.
Second, the bond and the caskets are both linked to the theme of fate and free will. Antonio's decision to borrow money from Shylock sets in motion a chain of events that leads to his downfall. Similarly, the suitors' decisions to choose a casket determine their fate in the play.
Third, the bond and the caskets are both used as dramatic devices to create suspense and conflict in the play. The audience is kept in suspense as to whether Antonio will be able to repay the debt, and which suitor will win Portia's hand.
In conclusion, the bond story and the casket are not independent in The Merchant of Venice. They are closely intertwined and play significant roles in the plot, themes, and dramatic structure of the play.