Swara is not divorcing Sanskaar because:
1. Saving Ragini's marriage
2. She doesn't love Lakshya anymore
3. She can't see her parents going through so much trouble from society because her
4. Maybe she has feelings for Sanskaar which she hasn't realised yet (keep reminding his love confession... when she could of remember all times he helped her out)
Even if she tells Sanskaar that she is keeping this marriage to save Ragini's marriage. Sanskaar will always treat Swara as a friend and not a wife. Swara is going to fall for Sanskaar deeply and no one can separate them... they will overcome every obstacle that comes their way (unlike swalak, failed the first step).