It sounds to me that the Probation Service are returning him to court for revocation and resentence on the grounds that the order is unworkable. If he has not been summoned for breach, I doubt the court will take too much of a dim view and will take into account that he has worked 47 of the given hours. Yes it is possible that he could go to prison, but I think it unlikely under the circumstances if the PS are recommending a curfew order instead.
He should get his solicitor to explain that the curfew order is doable for the time being, but once he returns to work, there will probably have to be a further hearing to change the hours.