Your argument is pretty contorted.
Your assumption is that since Smith was murdered the prophecy became moot. Using deductive reasoning skills this would assume 1) God is not smart enough (or shall be say omniscient enough) to have known that Smith would be murdered when he 'supposedly' gave this information to Smith or 2) Being all-knowing and omniscient he knew Smith was going to be murdered and lied to Smith so that Smith would think otherwise and then issued all of those unfulfilled prophecies. Now again using any College level 101 Logic course you are left with 1) God is dumb or 2) God is a liar.
In any case something very much less than God. Or there is a 3rd choice which is the one I choose and that is Smith was a false prophet and you have to be completely brainwashed not to see this. However on a positive note this convoluted thinking certainly does prove the Mormon God is not the God of the Bible as the God of the Bible IS all-knowing, omniscient, omnipresent and mighty enough to have known EXACTLY how Smith would meet his end.