The price reduction (£150 in UK) on the previously base retina iMac is bringing me nearer to a decision. But I am still on the fence re SSD v Fusion Drive. On balance, I probably prefer the convenience of a larger FD to the speed advantage of the SSD. But I hesitate over the cost consequences of the more probable failure of a FD beyond the 3 year point. So the question. If a FD fails, can the iMac work solely on the basis of external storage? Forgive my ignorance please.