Onething is for sure that Ganga has to remain Sagar's so she will not be married. With a lot of chaos happening in the serial and with such less time the following 2 possibilities may happen.
1. Sagar will come to know abt the truth about Rahul and maybe he will stop the marriage in last moment and some story of Rahul will come up.
2. I somehow have a feeling that maybe sagar will come to know and he will tell Ganga and ask her not to marry Rahul. But Ganga is committed and feels it matters less how Rahul is and wants to go ahead wit the marriage. At the brink when the marriage rituals are going on Sagar cannot stop himself and in order to stop the marriage will put Sindoor on Ganga's maang.
Then the truth of Rahul will come out and Ganga will disown the marriage but another big drama in the house and Kaveri/ Ganga track might start.
What say.....