Jesus Failed to Return as Promised

The first account of Jesus' prediction of his return is stated by Mark in chapter 13. Let's take a cursory glance and open it up for discussion...

1 And as he came out of the temple, one of his disciples said to him, “Look, Teacher, what wonderful stones and what wonderful buildings!” 2 And Jesus said to him, “Do you see these great buildings? There will not be left here one stone upon another, that will not be thrown down.”

3 And as he sat on the Mount of Olives opposite the temple, Peter and James and John and Andrew asked him privately, 4 “Tell us, when will this be, and what will be the sign when these things are all to be accomplished?”
According to Edward Adams in The Stars Will Fall From Heaven, these are two separate questions conjoined by the word καὶ, "and" (p. 140). The second question is a clear allusion to Daniel 12:6-7 as translated in the LXX (Mark: ταῦτα συντελεῖσθαι πάντα; cf. Daniel 12:7 συντελεσθήσεται πάντα ταῦτα), where Daniel is talking about the end of all things and the resurrection of the righteous and unrighteous (see 12:1-3).

5 And Jesus began to say to them, “Take heed that no one leads you astray. 6 Many will come in my name, saying, ‘I am he!’ and they will lead many astray. 7 And when you hear of wars and rumors of wars, do not be alarmed; this must take place, but the end is not yet. 8 For nation will rise against nation, and kingdom against kingdom; there will be earthquakes in various places, there will be famines; this is but the beginning of the birth-pangs.

9 “But take heed to yourselves; for they will deliver you up to councils; and you will be beaten in synagogues; and you will stand before governors and kings for my sake, to bear testimony before them. 10 And the gospel must first be preached to all nations. 11 And when they bring you to trial and deliver you up, do not be anxious beforehand what you are to say; but say whatever is given you in that hour, for it is not you who speak, but the Holy Spirit. 12 And brother will deliver up brother to death, and the father his child, and children will rise against parents and have them put to death; 13 and you will be hated by all for my name’s sake. But he who endures to the end will be saved.

14 “But when you see the desolating sacrilege (RSV; NASB, "abomination of desolation;" NIV, "the abomination that causes desolation") set up where it ought not to be (let the reader understand), then let those who are in Judea flee to the mountains; 15 let him who is on the housetop not go down, nor enter his house, to take anything away; 16 and let him who is in the field not turn back to take his mantle. 17 And alas for those who are with child and for those who give suck in those days! 18 Pray that it may not happen in winter. 19 For in those days there will be such tribulation as has not been from the beginning of the creation which God created until now, and never will be. 20 And if the Lord had not shortened the days, no human being would be saved; but for the sake of the elect, whom he chose, he shortened the days. 21 And then if any one says to you, ‘Look, here is the Christ!’ or ‘Look, there he is!’ do not believe it. 22 False Christs and false prophets will arise and show signs and wonders, to lead astray, if possible, the elect. 23 But take heed; I have told you all things beforehand.
In these verses Edward Adams argues that Jesus has answered the first question about the destruction of the temple and what his followers should do when they see these things.
24 “But in those days, after that tribulation, the sun will be darkened, and the moon will not give its light, 25 and the stars will be falling from heaven, and the powers in the heavens will be shaken. 26 And then they will see the Son of man coming (ἐρχόμενον) in clouds with great power and glory. 27 And then he will send out the angels, and gather his elect from the four winds, from the ends of the earth to the ends of heaven.
The events previously described (vss. 5-23) are distinguished from the ones that follow in this chapter. Edward Adams says "there is no indication of a temporal gap between the close of the tribulation and what is about to be described. What takes place 'after that tribulation' can only be the eschatological climax" (Adams, p. 146). The Greek word translated "coming" (ἐρχόμενον) in reference to Jesus can also mean "going." But this is clearly an allusion to Daniel 7:13, and Zechariah 14:5, so it fits better in the context to be translated as "coming." Adams also documents that this apocalyptic language was taken quite literally by the ancient people of that day when predicting the end of all things. They literally believed the sun and moon will be darkened, and that the stars will fall from the sky at the end of times.
28 “From the fig tree learn its lesson: as soon as its branch becomes tender and puts forth its leaves, you know that summer is near. 29 So also, when you see these things taking place, you know that he is near, at the very gates. 30 Truly, I say to you, this generation will not pass away before all these things take place. 31 Heaven and earth will pass away, but my words will not pass away.
About verse 30, Adams writes, "It is virtually certain that 'this generation' means the generation living at the time of utterance. The time frame in this verse is thus the lifetime of Jesus' own contemporaries." (p. 164). Verse 31 is related to the whole discourse for even though "creation will be dissolved; Jesus word's will endure" (Adams p. 162). D. Sims as quoted by Adams: "A more clear expression of the end of the present cosmic order would be difficult to find" (p. 162).
32 “But of that day or that hour no one knows, not even the angels in heaven, nor the Son, but only the Father. 33 Take heed, watch; for you do not know when the time will come. 34 It is like a man going on a journey, when he leaves home and puts his servants in charge, each with his work, and commands the doorkeeper to be on the watch. 35 Watch therefore—for you do not know when the master of the house will come, in the evening, or at midnight, or at cockcrow, or in the morning— 36 lest he come suddenly and find you asleep. 37 And what I say to you I say to all: Watch.”
While Mark's Jesus says this will happen in his generation, he also says no one knows what specific day or hour.

The point is that Jesus did not return as promised in his generation, period. Forget all the talk about not knowing the day nor the hour. We were told he was to return in his generation, and that generation has come and gone.