Apostle Paul wrote his epistles prior to AD70..The partial hardening of The Jews mentioned in Rom 11:25 ended in AD70 after which the Nation was destroyed as prophesied by Jesus Mat 24:15 wherein He makes reference to Daniels Prophecy..
The fullness of the Gentiles coming in, to which the Apostle refers = (the gospel going to the Gentiles) it is not about the last Gentile to be saved and then coming the Jews turn again to be saved.. The scripture is very clear, for the Gospel is preached to all men Jews first..
The prophesied destruction of the nation happened back then in AD70 with "the one who came making desolate, even until a complete destruction"
Dan 9:27, Mat 24:15
The Roman army being the people of the "prince" (Titus, son of the emperor Vespartian) Dan 9: 26..
Despensationalists wrongly imply that event of Daniels prophecy to the modern state of Israel at a future time, saying that the last week (the seventieth week) of Daniels prophecy was not part of the preceding sixty nine weeks.. in other words They break the continuity of the prophetic flow placing a 2000 year gap between the sixty-ninth and the seventieth week..
All prophecy must be understood in the light of the Gospel and Epistles..
Understanding what the symbolic "Olive Tree" be, Nullifies the dispensational theory of a future salvation post-return of Christ for Jews or any person for that matter, for at the end comes "the judgment of the Living and the dead".... See: post (What of the end when Jesus returns)
The Olive Tree of Rom11 is "The commonwealth of Israel" For it is God who grafts both Groups (Jews and Gentiles) into His "commonwealth of Israel" to save them all as 'one people' under the headship of Christ by grace through faith prior to the end and the return of Christ..
The Apostles taught no other means of salvation but by grace through faith. That salvation was also spoken by the prophets as the "New Covenant"
There is only the "one Hope of Israel" for which Paul endured prison Acts 26:6,7, 28:20.. That one hope of Israel is the "promise given to the Fathers" Acts 26:6 realised by the new covenant within the "commonwealth of Israel" The redeemed of the Lord purchased by the Blood of Christ..
See: post (Abraham Father Of Many Nations)