Marriage is old, much older than recorded history. Artifacts from pre-history suggest that marriage has existed as long as there's been hierarchical society, and it's existed in literally every single culture, almost every tribe, everywhere. It's not always been about man + woman either, I know off the top of my head that in some places in Africa
a woman can be the husband and marry another woman, taking on the male roles if there were no other suitable males available or if she was the most suitable for the husband role. This practice has existed for hundreds of years. All traditions of "regular" marriage are observed, the female husband's family even recieves dowry.
Anyway, yeah, marriage is to do with society, not religion or money. I'm obviously not the wife type, but I think that where there's society, there's going to be marriage. Even if religion ceased to be a factor in society, I believe marriage would remain.