And Sadhna is brought back in a double role to Alekh's life, the story might not have any charm...and if Sadhna is brought back as her daughter, then we expect a leap. We are not prepare for any options like these.
My guess is either Sadhna suffers an accident post godh-bharai or she is already informed by the doctor that her delivery might danger her life, but she would go ahead with the child, when she sees everyone so happy and waiting for the child and also if anything happens to her, her jiji is always there to give her child "mother's mamta" and that the child will be treated as the apple of the eyes by everyone in her absence...Vasu, Inder, Mama, Mami, Alekh, Ranveer, Ragini. So her child will never feel her absence. Probably, she might sacrifice her life...I base my assumption on Mamaji's dialogue to Sadhna "why she is looking so pale"...and Mamiji's "she is the one uniting both the families"...
If someone has to die, it will be Sadhna, as her death will be more meaningful and a tracj can be built around that ..from a ralistic point of view, her job is done, she came to RH to save the family and to get Ragini married to Ranveer, she found Alekh abnormal and she helped Alekh to become normal and self sufficient, she changed Vasu's arrogance to humbleness, she solved the recent Karan case...she has executed each and every of her "Karma' with every sincerity. No pain, no mental torture could take away the selflessness from her. She touched each ones life and filled their lives with happiness, sometime even without their knowing that. She is a true follower of Karma, all the other people whose lives she touched, they now have to carry the good work of hers.
Everone will be shattered, but everyone has one support to cling to except Alekh. Only unfortunate incident is that Alekh is again left shattered...he is so unfortunate, and so will the baby be...who could not get to see such a selfless mother...