Your IVA will officially end once the termination notice is issued --- as with a completion certificate, this can take a few months. You will be removed from the Insolvency Register up to three months from the date the termination notice is issued. 'Normal' communications between you and your creditors can start, again, once the termination certificate is issued.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014 http://foggy.blogs.iva.co.uk
It takes usually 8-12 weeks to set up a DRO so you should be getting this process underway now. don't wait until the IVA fails.
It would be very unusual for you to be harassed by a creditor immediately after your IVA fails. It will take most of them a month or two to realize what has happened. If you are, then ask your DRO adviser about a breathing space, which should stop any creditor contact for 60 days.