Could people in ancient times tell whether someone was still alive after being stoned?

Ancient people were not stupid; they had a pretty good idea whether life was left in a body. Those who stoned Paul at Lystra supposed he was dead, and the account treats the stoning as putting Saul to death for all practical purposes.

Les explains that according to the Jewish system of execution, the Jews at Lystra literally felt they had put the man to death. After stoning Paul, they drew him out of the city, supposing he had been dead. Les notes that the ancients were not that stupid and had a pretty good idea if there was life left in a body, so he concludes that for all practical purposes Saul was put to death as a result of this stoning. Then in Acts 14:20, Paul miraculously stood up on his feet without any help from any outside source.

Acts 14:19

And there came thither certain Jews from Antioch and Iconium, who persuaded the people, and, having stoned Paul, drew him out of the city, supposing he had been dead.

Could the people of Paul's day tell whether someone was actually dead?

People in Paul's day could generally discern whether someone was actually dead. The ancients were not stupid; they had a reasonably good idea whether life remained in a body. Those who stoned Paul therefore supposed he was dead, and for all practical purposes Saul was put to death by that stoning.