If that sign is abrogated...
If that sign is abrogated, its inherent benefit would be lost; nothing could take its place to preserve that benefit. Allah is not like His creatures, nor is His knowledge like theirs. His knowledge does not change with the changes in external factors.
It is not that one day He knew one thing and issued an order according to that knowledge; then next day the knowledge changed and He became aware of another factor which He did not know before, and therefore He had to cancel the previous order, replacing it with a fresh one. Such inconsistency is not worthy of Divine Sublimity.
Of course, it is all right for us mortals, because we cannot comprehend all the aspects of an affair; and as a result of this incomplete knowledge, our decisions are frequently changed and amended. But we should not compare Divine Knowledge without limited and defective perception. Here it is necessary to point out that such an objection arises from a notion that the power of Allah is neither comprehensive and all-encompassing nor unrestricted and unconditional.
Second: Accepted that the Divine Power is all-encompassing and limitless. But once a thing is created it goes beyond the sphere of that power, and cannot be changed. Even in our case, we have power to do or not to do a certain work - so long as we have not done it; but once we have done it, it becomes an essential being, and goes beyond the limits of our power.
This argument is based on the rejection of the all-encompassing ownership of Allah; it presupposes that once Allah has managed a certain affair in a certain way, He cannot change that arrangement in another way. This Jewish belief is portrayed in the verse: And the Jews say: “The hand of Allah is tied up” (5:64). Allah replies to the first objection with the question: “Do you not know that Allah has power over all things?” He certainly has power over all things.
Therefore, He may replace a sign with an equally good or even a better sign. The second objection is dealt with by the next question: “Do you not know that Allah's is the kingdom of the heavens and the earth, and that besides Allah you have no guardian or helper?” Allah is the Owner of the heavens and the earth; He can do whatever He likes with His property.
No one besides Him owns any thing; otherwise, that owner could interfere in the management of Allah or put restriction on His authority and control. None else owns any thing - neither in his own rights nor even when Allah gives to him a partial ownership.