They are killed instantly (and painlessly, don't worry). But also, the transaction will reflect as OOP (Out of Policy) in the Admin Dashboard and show the price difference from the policy limit along with the other transaction details.
Shep's open booking platform means you won't be prevented from booking out of policy. Continue with your selection and a pop up will ask you to confirm your booking choice and send a notification to your company's administrator. You can then finish the booking process.