Good response, and I thought you might say that. 😉
It had occurred to me after reading Heiser as well that why would the human population that enters the resurrection simply be maintained rather than expanding? When you look at how vast the universe is, it seems to me that it might be God's intent that we go and fill it, and that probably requires more than those redeemed humans from this life who enter the resurrection.
It just seems odd to contemplate sex without marriage (as a Christian; I know unbelievers and adulterers do it all the time, in this life). Heiser accepts the idea that "the sons of God" in Scripture are angels and that they can and have in the past reproduced with human women, so if that's true, why wouldn't there be sex in the next world?
Thanks for responding and I hope you are well.