Can never tell when your time is up.
I note two men died running a half marathon in Cardiff over the weekend. One in his twenties, the other in his thirties. I thought fit people ware supposed to live longer.
Even if you did have a heart attack through over exertion at the end of a race, you'd think there'd be expert help at the finish line. People that age shouldn't die if there is a defibrillator on hand, and I hope there was.
Defibrillator is only of any use for correcting / restarting the heart's electrical activity. If it was due to a blood clot, even if you were in hospital there is only about a 50% chance of them being able to revive you!
Heart attacks are most common in unfit people and ultrafit people it is a bit of a bathtub curve with the unfit side steeper and higher. Unknown heart defects including a hole in the heart from when the hole between the two sides doesn't completely close shortly after birth can manifest themselves during the high stress just before or during a race. I know two untrafits that have died just before starting a race.
Sad what has happened in that accident in the US but their annual death rate is sadly much higher than in the UK.