Apparently, McDowell worked on the topic as a dissertation and turned it into a book. Alas, the book is an academic print run and costs $119.95 and not likely to be purchased by the average reader!
McDowell has blogged about some of the content of the book at his web page and one can listen to the STR podcast.
Briefly, the premise of his project was that he (and most of us) have often heard that most of the Apostles died for their faith. McDowell decided to try to track down the historical data to see if this assertion is born out.
As one might imagine, trying to find evidence for something that happened 2000 years ago isn’t easy. In the podcast, he discussed the nature of the evidence for the deaths of Peter and Paul, James the brother of John, and James the brother of Jesus. He, along with other history scholars, rate the evidence for these as pretty good.
The support of what happened to Thomas and Andrew is not as strong but on balance is plausible. The data on the remaining apostles is not conclusive and sometimes contradictory.
He and Greg Koukl also discussed the data on the Apostle John. The main view is that he died of old age on while in exile on Patmos or shortly after leaving Patmos. However, there is a subset of scholars who cite some suggestive evidence he might have died for his faith somewhere in the time period covered by the Book of Acts. He appears active in early chapters in Acts and then suddenly isn’t mentioned. That is an argument from silence but scholars point to some external (non-Biblical) sources that also point to a possible early death.
Whether all the Apostles actually died as a direct result of their faith, is not knowable from the historical data. However, what can be said is the following:
(1) The NT writings suggest that suffering for the faith was something the believers should expect and in some case had already experienced.
(2) The message of the faith and the motivation to persevere was the belief in the Resurrection of Jesus.
This does NOT prove the resurrection of Jesus but it does prove that the resurrection was central to the early Christian message and motivation for the faithfulness of the first Christians.