All of this comes directly from Paul.Mark 13:
26 “At that time people will see the Son of Man coming in clouds with great power and glory. 27 And he will send his angels and gather his elect from the four winds, from the ends of the earth to the ends of the heavens.
28 “Now learn this lesson from the fig tree: As soon as its twigs get tender and its leaves come out, you know that summer is near. 29 Even so, when you see these things happening, you know that it is near, right at the door. 30 Truly I tell you, this generation will certainly not pass away until all these things have happened. 31 Heaven and earth will pass away, but my words will never pass away.
32 “But about that day or hour no one knows, not even the angels in heaven, nor the Son, but only the Father. 33 Be on guard! Be alert! You do not know when that time will come. 34 It’s like a man going away: He leaves his house and puts his servants in charge, each with their assigned task, and tells the one at the door to keep watch.
35 “Therefore keep watch because you do not know when the owner of the house will come back—whether in the evening, or at midnight, or when the rooster crows, or at dawn. 36 If he comes suddenly, do not let him find you sleeping.
Obviously Paul said this was going to happen in his lifetime, but it didn't. The writer of Mark knew that. But he's just putting Paul's words into Jesus' mouth anyway.1 Thessalonians 4:
15 For this we declare to you by the word of the Lord, that we who are alive, who are left until the coming of the Lord, will by no means precede those who have died. 16 For the Lord himself, with a cry of command, with the archangel’s call and with the sound of God’s trumpet, will descend from heaven, and the dead in Christ will rise first. 17 Then we who are alive, who are left, will be caught up in the clouds together with them to meet the Lord in the air; and so we will be with the Lord forever. 18 Therefore encourage one another with these words.
1 Thessalonians 5:
1 Now concerning the times and the seasons, brothers, you do not need to have anything written to you. 2 For you yourselves know very well that the day of the Lord will come like a thief in the night. 3 When they say, “There is peace and security,” then sudden destruction will come upon them, as labor pains come upon a pregnant woman, and there will be no escape! 4 But you, beloved, are not in darkness, for that day to surprise you like a thief; 5 for you are all children of light and children of the day; we are not of the night or of darkness. 6 So then let us not fall asleep as others do, but let us keep awake and be sober; What I say to you, I say to everyone: ‘Watch!’”
Besides, I am confident that the "desolating sacrilege" refers to the statue described by Pilate in his account of the "Caligula Crisis", which occurred in 40 CE. So the writer already knew that that didn't really happen. This wasn't an attempt to make some real prophecy.
By the time the writer was writing, the Caligula Crisis was long over and Paul was long dead. The writer knew that and the writer knew that the predicted Parousia never occurred.
I don't know exactly when the Gospel of Mark was written, but I know that Mark 13 wasn't a real prophecy nor an attempt at a real prophecy.