Unfortunately, sending a 'heavy mob' in to ask questions - will not give you the answers. Everyone will now be out to protect their own @rse and point the blame. They will have only been there a short time, they were told to do this, they were in the process of checing procedures when X did Y and the Z happened. etcetera.
If the company had a strong line of communication, where the senior IT mgmt were KNOWN and VISIBLE? Then you can get the information you need.
Since it is clear that it was an utter failure, at every level, You might be better off starting form scratch. Trying to work out what went wrong and then patching it? Again? But, as davidjohnson6 says, the 'heavy mob' will be only too glad to specify a new system. That is, one that no one at the top understands. Oh, that looks like what they already have.
Last edited by PAXboy; 31st May 2017 at 22:58.