I see a lot of speculation and "what ifs" there.
Absolutely.
Arguably he did know about the destruction of Jerusalem.
So wouldn't he be likely to mention it?
Why would he know about the deaths of Peter and Paul? When did they die? Where did they die? What documentary evidence do you have for your answers?
In 2 Tim 4:6 Paul writes that he already is being poured out like a drink offering and the time has come for his departure. He goes on to say, v 11, that 'only Luke is with me'.
Luke was also with him earlier, when he sent his greetings to the Colossians (2 Col 4:14).
Two clues that Luke wrote his gospel under Paul's influence are:
- 1 Corinthians 11:23-25 cf Luke 22:17-20 where there are several similar phrases in their descriptions of the last supper.
- Luke 24:34 cf 1 Corinthians 16:4,5 where they both mention that Peter was the first man to whom Jesus appeared after he rose.
So Luke is the author of Luke/Acts and journeyed with Paul, who had met the apostles. He stayed with Paul during his imprisonment, up until the time Paul was aware of his impending execution. Luke concludes Acts abruptly without saying what happened to Paul after the two year house arrest.
Luke could, then, have waited a long time to write Acts, but we know that he wrote his gospel before that, so it was some time during Luke's life. The main point is that he was in the inner circle of Paul's companions from Acts 16 onwards. He met the brothers, the elders and James in Jerusalem (Acts 21:18). Notably he appears to have witnessed Paul bringing Eutychus back to life (Acts 19:10). Surely, then, he had access to eyewitness accounts, oral and written, and witnessed a miracle himself.