I think break up will be initiated from Sona's side this time. This will break Dev to the core and maybe put some senses that he cannot take Sona for granted everytime just because she loves him immensely.
Sona will conceive and maybe Ishwari will try again to bring Sona back in Dixit house but Sona will not agree and will file for divorce. Dev will then come to know about prenup and then maybe at that point he may realize Ishwari's real intentions. He may go away from Dixit house or isolate himself from everyone and then the redemption starts of winning back Sona and bringing her back with dignity.
On the other side, they might show problems occurring in Dixit house with Neha, Nikki etc which reminds them constantly about the goodness of Sonakshi and how she used to handle situations and help them sort it out. Radha Rani's evil doings will be out in open and maybe then Ishwari's redemption may start of realizing what she has lost.