"people" would be better to use then "generation" as it is clearer. The people that see the events/signs Christ described would see all the things he described, and that includes the second coming and rapture (angels gathering the saints).
The point is
not that everyone would see all the events. The point is that not every one would have died who was a witness to 1948. What age defines the generation that understood 1948? Age 5? Age 15? Age 25? Age 35? Jesus' point is that two or more witnesses will still be alive who understood 1948 when it happened.
The same principle applied to the first coming. The generation at the end of the 69 weeks, mentioned in Daniel had all passed away except Simeon and Anna mentioned in Luke 2.
"And, behold, there was a man in Jerusalem, whose name was Simeon; and the same man was just and devout, waiting for the consolation of Israel: and the Holy Ghost was upon him. And it was revealed unto him by the Holy Ghost,
that he should not see death, before he had seen the Lord's Christ."
"And she coming in that instant gave thanks likewise unto the Lord, and spake of him to all them that looked for redemption in Jerusalem."
That generation had not passed away until they saw the Messiah. Seems the majority were already dead. Not even Herod nor the religious leaders were prepared. That generation when Jesus was born, was not prepared for the Messiah. They had to go to the Scriptures to even see where Jesus would be born.
"And when he had gathered all the chief priests and scribes of the people together, he demanded of them where Christ should be born. And they said unto him, In Bethlehem of Judaea: for thus it is written by the prophet,"
So we see two different generations. One had mostly passed without seeing the Messiah but had been waiting. The next generation or two generations later were not waiting for the Messiah nor prepared for the arrival.
Seems history will repeat itself. People have been talking about this for generations. That first generation, will have all passed except those last few witnesses. The actual generation will not be prepared, because the point will have been lost on them, as to what will happen. Now many teach future generations it all happened in the first century, and nothing will happen nor change in their lifetime.