Re: what is the reward of marriage?
Even if a woman whores around, no one on earth knows for sure whether or not she'll go to paradise or hell. That is up to our Lord alone.
Allah SWT is Most Merciful, and shows the greatest of mercy for the smallest of deeds.
2 hadiths from Sahih Muslim come to mind.
Book 026, Number 5578:
Abu Huraira reported Allah's Messenger (may pace be upon him) as saying: A prostitute saw a dog moving around a well on a hot day and hanging out its tongue because of thirst. She drew water for it in her shoe and she was pardoned (for this act of hers).
Book 026, Number 5579:
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: There was a dog moving around a well whom thirst would have killed. Suddenly a prostitute from the prostitutes of Bani Isra'il happened to see it and she drew water in her shoe and made it drink, and she was pardoned because of this.