do i really need this

hi all,
well the rear box fell off the discovery 300 tdi this morning,no hint just decided it had enough and went for a wall along the road and got splattered by a passing car.
the exhaust sounds about the same not a tad noisier at all so can i just put a piece of pipe o whats left and not bother about the box or is it a mot fail??
any ideas anyone?? bearing in mind that it did break off next to the support bar