Hi Alex,
This is a tough one to explain to anyone deeply entrenched in carnal thinking. Most of us have a natural instinct (carnally) to cling to our physical life. But Jesus said:
For whoever would save his life will lose it, but whoever loses his life for my sake will find it.
Matthew 16:25
Thousands of people lived and died to fulfill scripture and become a message to God's Elect. They themselves did not receive the promises:
Others suffered mocking and flogging, and even chains and imprisonment. They were stoned, they were sawn in two, they were killed with the sword. They went about in skins of sheep and goats, destitute, afflicted, mistreated-- of whom the world was not worthy--wandering about in deserts and mountains, and in dens and caves of the earth. And all these, though commended through their faith, did not receive what was promised, since God had provided something better for us, that apart from us they should not be made perfect.
Hebrews 11:36-40
What were the meanings and purposes of the lives of those who lived in Old Testament times?
I want you to know, brothers, that our fathers were all under the cloud, and all passed through the sea, and all were baptized into Moses in the cloud and in the sea, and all ate the same spiritual food, and all drank the same spiritual drink. For they drank from the spiritual Rock that followed them, and the Rock was Christ. Nevertheless, with most of them God was not pleased, for they were overthrown in the wilderness. Now these things took place as examples for us, that we might not desire evil as they did. Do not be idolaters as some of them were; as it is written, "The people sat down to eat and drink and rose up to play." We must not indulge in sexual immorality as some of them did, and twenty-three thousand fell in a single day. We must not put Christ to the test, as some of them did and were destroyed by serpents, nor grumble, as some of them did and were destroyed by the Destroyer. Now these things happened to them as an example, but they were written down for our instruction, on whom the end of the ages has come.
1 Corinthians 10:1-11
I know this wouldn't satisfy your friend. Aside from the physical, these things that happened in the scripture cited in your post, are spiritual lessons/messages. These towns/people were following after other gods....all that is in us, which follows after other gods, which is carnal and sinful must be COMPLETELY destroyed....not one bit of the carnal man must survive.
Behold, these, on Balaam's advice, caused the people of Israel to act treacherously against the LORD in the incident of Peor, and so the plague came among the congregation of the LORD. Now therefore, kill every male among the little ones, and kill every woman who has known man by lying with him. But all the young girls who have not known man by lying with him keep alive for yourselves.
Numbers 31:16-18
I believe "the young girls" is referring to the Elect:
It is these who have not defiled themselves with women, for they are virgins. It is these who follow the Lamb wherever he goes. These have been redeemed from mankind as firstfruits for God and the Lamb
Revelation 14:4
I feel a divine jealousy for you, for I betrothed you to one husband, to present you as a pure virgin to Christ.
2 Corinthians 11:2
You see? When you begin to discern these things spiritually, they take on a whole different layer of meaning. But good luck trying to show this to your friend, who is obviously seeing things only physically.
Pray for his eyes to be opened, only God can make him see.
Peace to you,
Diana