If you choose to withdraw funds within the first year then your Welcome Share balance will decrease (not below zero) upon a withdrawal from your Referred Account based on the following formula:
Number of Shares Returned to IBKR= (Withdrawal Value / Net Deposit Value Before Withdrawal) x Welcome Share Balance Before Withdrawal
If you withdraw funds after the first year then your unvested IBKR shares will remain. However, if you initiate a close request prior to the IBKR shares being vested then you will forfeit all shares.