The basis of swarna and her husband is just wrong to start off with and so it will never happen as they intended. All wrong!
As for Rana and gayatri it's whole different story gayatri is devoted to her husband and loves him. Whether he loves her back or not he has a sense of possessiveness for her. She is HIS queen his wife, something we saw with the wilkinson thing. If it really came down to it and gayatri asked for a child from him as a king i think Rana put aside everything aside even his dead wife and give the throne a future. Of course that's not the way we want it to go ..
Rana is going topple in his steps at one point or the other He's human after all and now he has a new queen and wife it takes only one slip of the heart ..