I don’t go around looking for arguments, so I don’t know what failed prophecies these people are looking at. But, you’re right, they deserve an answer.
What I haven’t heard mentioned so far is the whole issue of how a prophecy is fulfilled.
Maybe they don’t recognize that a prophecy has been fulfilled. I know a book called “Why the Jews Rejected Jesus” that goes into this sort of thing, arguing both points, that the prophecies have been fulfilled in the past and that the claims of Christianity are therefore untrue.
But, I couldn’t finish reading that book, because I thought it was wrong on so many points that I didn’t have to read it to the end.
I don’t think that peripheral prophecies about the Nile drying up are very important. I don’t recall reading that one. There are different style of writing in the Old Testament. Today, with the aid of a Jewish commentary, I realized how King David made a sarcastic reply to a woman named Michal. Sarcasm in the Bible? You bet. Quite a bit more than you might think.
The big prophecy is that of the coming of the Messiah, the anointed one, who would re-establish the monarchy and reign forever and build the third temple. Christians see that as fulfilled IN Jesus. Jesus is the new Temple. That Jewish book dismisses statements like this, complaining that Christians have spiritualized everything. Well, that’s how it turned out! Things were spiritual in the first place. Read Jeremiah 7:21 and down a few verses. God wanted a change of heart in the Israelites, not a spirit-less cult of obscure rituals.
The Pontifical Biblical Commission wrote a lengthy introduction to this subject of the relation of the Old and New Testaments, which I link here and to which I refer you for a high level discussion