The bond is to secure payment of the civil judgment against Trump, and merely stops collection efforts pending the appeal. If he loses the appeal, then the bond pays and the bond company gets reimbursed by the collateral posted by the judgment debtor.
If he wins the appeal, the judgment debtor no longer has a judgment against him, and the bond is discharged, but the judgment debtor loses the premium paid for the bond (like an insurance policy).
This is not in the nature of a criminal bond to guarantee appearance in court.
Thanks for the details.