If we go into the Old Testament, you and I will really need to become scholars! Not saying that isn't a good thing to do, but it takes great knowledge to know what they are talking about and we could go on picking out individual verses that seem to point one way or another forever. (I do believe that the verse you are referencing in Isaiah is pointing to people currently under control of Islam in Sela. The question is why are they rejoicing?)

Then there is this much more interesting list of Muslim territories in Ezekiel:

Son of man, set thy face against Gog, the land of Magog, the chief prince of Meshech and Tubal, and prophesy against him, and say ‘Thus says the Lord GOD: “Behold, I am against you, O Gog, the prince of Rosh, Meshech, and Tubal. I will turn you around, put hooks into your jaws, and lead you out, with all your army, horses, and horsemen, all splendidly clothed, a great company with bucklers and shields, all of them handling swords. Persia, Ethiopia, and Libya are with them, all of them with shield and helmet; Gomer and all its troops; the house of Togarmah from the far north and all its troops—many people are with you. After many days you will be called to arms. In future years you will invade a land that has recovered from war, whose people were gathered from many nations to the mountains of Israel, which had long been desolate. They had been brought out from the nations, and now all of them live in safety. You and all your troops and the many nations with you will go up, advancing like a storm; you will be like a cloud covering the land. -- Ezekiel 38

I think its best to focus on the only thing that matters:

The essential point of Christianity is Jesus' death and resurrection is the key to Heaven. Muhammad denied this explicitly.

This is serious. It means that trusting Muhammad is turning your back on what Jesus tells us is the only way to eternal life.

All the rest is an interesting exercise. Since Muhammad denied this sine qua non of Christianity, everything else he said is moot.

The fate of nearly two billion people hangs in this balance.