The O.T. teaches that there is a future for Israel. What about the N.T.?  Did the destruction of the Temple in A.D. 70 spell the doom for them as a nation?

Jesus said,  Luke 21:24  And they shall fall by the edge of the sword, and shall be led away captive into all nations: and Jerusalem shall be trodden down of the Gentiles, until the times of the Gentiles be fulfilled.

This does not imply their destruction, but their captivity UNTIL the times of the Gentiles are fulfilled.  They certainly have been in captivity for the past 2000 years. They have been a hated and persecuted people.

Matt. 23: 37, 38  O Jerusalem, Jerusalem, thou that killest the prophets, and stonest them which are sent unto thee, how often would I have gathered thy children together, even as a hen gathereth her chickens under her wings, and ye would not!  Behold, your house is left unto you desolate. For I say unto you, Ye shall not see me henceforth, till ye shall say, Blessed is he that cometh in the name of the Lord.

Here they have rejected Him, so He says your house (temple) will be empty. This happened in A.D. 70. It has not yet been rebuilt, but plans are made to do so.  He set a time limit on this desolation. UNTIL  V.39  Ye shall not see me henceforth, till ye shall say, Blessed is he that cometh in the name of the Lord.

He even says here that they will see Him again.  Zechariah 12:10 And I will pour upon the house of David, and upon the inhabitants of Jerusalem, the spirit of grace and of supplications: and they shall look upon me whom they have pierced, and they shall mourn for him, as one mourneth for his only son, and shall be in bitterness for him, as one that is in bitterness for his firstborn.

Matthew 19:28  And Jesus said unto them, Verily I say unto you, That ye which have followed me, in the regeneration when the Son of man shall sit in the throne of his glory, ye also shall sit upon twelve thrones, judging the twelve tribes of Israel.

This regeneration is future. It is when He sits upon His throne of glory. He is not on that throne yet.  Matthew 25:31 When the Son of man shall come in his glory, and all the holy angels with him, then shall he sit upon the throne of his glory:  Then, the twelve will sit and rule over Israel.

The disciples believe it. Listen to what they asked Him; Acts 1:6 When they therefore were come together, they asked of him, saying, Lord, wilt thou at this time restore again the kingdom to Israel?

He did not say, I am through with this nation, but, V. 7  And he said unto them, It is not for you to know the times or the seasons, which the Father hath put in his own power.

God is now calling out a people from among the Gentiles. It is called the "fulness of the Gentiles" Rom. 11:25.  There Israel is blinded because of their unbelief UNTIL the fulness comes in.

11:25  For I would not, brethren, that ye should be ignorant of this mystery, lest ye should be wise in your own conceits; that blindness in part is happened to Israel, until the fulness of the Gentiles be come in.

Then:
26  And so all Israel shall be saved: as it is written, There shall come out of Sion the Deliverer, and shall turn away ungodliness from Jacob:
27  For this is my covenant unto them, when I shall take away their sins.

Prophesies in the N.T. that are yet to be fulfilled:

Matthew 2:6  And thou Bethlehem, in the land of Juda, art not the least among the princes of Juda: for out of thee shall come a Governor, that shall rule my people Israel.

This did not happen yet.

Luke 1:32  He shall be great, and shall be called the Son of the Highest: and the Lord God shall give unto him the throne of his father David:
Neither has this happened.

Acts 2:30  Therefore being a prophet, and knowing that God had sworn with an oath to him, that of the fruit of his loins, according to the flesh, he would raise up Christ to sit on his throne;

Not yet, either.

Numbers 23:19  God is not a man, that he should lie; neither the son of man, that he should repent: hath he said, and shall he not do it? or hath he spoken, and shall he not make it good?

God will and is keeping His promises to Israel.