When your creditors agree to your proposal at the Meeting of Creditors, they are agreeing to only accept a certain amount of the debt back, to stop all interest and charges and to not contact you any more, they have to deal with your Insolvency Practitioner from then on.
Therefore once your IVA is completed satisfactorily, they debt is literally not there any more, and so they have no legal right to chase you any more. Bear in mind you must include all your creditors, as any not contacted and made aware of the IVA are outside the proposal and so can still chase their debt. You are not supposed to obtain any further unsecured credit whilst in the Individual Voluntary Arrangement, how ever if you do, this would also not be part of the IVA agreement and this debt would remain after your IVA is complete.