Your employee benefits will be removed soon after leaving, you'll then get notified and be on ex-employee broadband with no discount or contract.
You can then renew with a discount or switch, if it bothers you that much you could ring in and request the account closed with 30 days notice.
Call the BT Options Team 0800.800.030
Complete a WLTO to your new provider and BT will soon send you a final bill? 🙂