The plot of the show is about a woman proving that she doesn't need to keep staying in an unwanted relationship to survive. If the divorce would have been cancelled, it would send a message that ultimately a woman should forgive a man if he repents, however wrong he might be.
The point is not to ask for forgiveness, but to not make the mistake at the first place.
Vanraj didn't have a one-night stand. I don't justify it either but that is an actual mistake and not a consensual EMA. He had a full-fledged affair with his colleague, while taking his wife for granted, enjoying benefits from both of them and would have continued if he wasn't caught. Plus not to forget his emotional abuse and gaslighting to Anupamaa, which is unforgivable even without an EMA.
Few weeks of pampering Anupamaa assuming with full-entitlement that she will return doesn't compensate for so many years of abuse.
16