As far as the word forever is used in reference to the Jews and their religion, you should know that forever as used in the Old Testament frequently refers simply to "an indefinite time period" vice literally for eternity. In other words, the promises given to the Jews were predicated on their obedience, which they failed at. The Bible teaches that the church of Christ is spiritual Israel now. The Romans destroyed the temple along with Jerusalem in 70 AD, forever taking away the sacrifices. This is the abomination of desolation spoken of by Jesus.
As far as the gospel being preached to all the world, that requirement was fulfilled in the book of Acts (Acts 1:8). In fact, as the book closes, we find the gospel has travelled from some remote outpost of the Roman Empire, all the way to the seat of civilization.
"Also, after the sack of Jerusalem the entire world did not see Jesus return " What you missed was that there is no specified time, long or short, occuring in between what happens in verse 29 and 30. IE verse 30 could come 1 hour after or 2000 years after verse 29.
The Bible has no such doctrine as contained in the popular "Left Behind" series. There is not going to be an earthly reign of Jesus for 1000 years ("My kingdom is not of this world"). The temple was not promised to be rebuilt. The Bible does not teach that a long period of time passes between the so-called rapture (word is nowhere in the Bible) and when Jesus comes again. It is all a bunch of false teaching resulting from taking figurative things too literally, and failing to proper contexutalize, which will not stand up to proper scrutiny.
May God's richest blessing chase you down.