Not sure if you can start a new claim if you ask for a Mandatory Reconsideration?
Have they given him an option to ask for a Mandatory Reconsideration? Was he switching from DLA? Best bet is too ring them and find out his options and it could be worth going for the Mandatory reconsideration.
Did he get help to complete the form and did if he have to wait for that help? If he gets a new form I would recommend ringing them straight away to request for an extension to the two weeks they give. They will normally give two weeks extra straight away, but I appreciate your friend will want to get it in straight away if their money has been stopped.
Would definitely be worth contacting local money advice service or CAB too.