i don't think it's the divorce, or rather the idea of it, that bothers her that much. She doesn't care so much about it as far as her personal feelings, and her life after it, are c oncerned. Yeah, it'll take some getting used to, but she'll get over it.
She's always, however, protected her children from such pain. And she feels it will be the epitome of pain and destruction for her children if he was to divorce her. And that too, to replace her with his sister.
There's also the fear of the unknown. Remember, she has seen Uttara replace her in her household with the chores, replace her as a wife even, but the one place she can't be replaced, that she can not watch silently while replacement takes place is that of a mother. They're her kids, and they better stay that way.
I am a mom, and I can tell you that once you create that bond, there's nothing like it. Nothing. A divorce one can get over, eventually. But if someone threatens to replace you wholly, your identity as you define it by way of motherhood, then that can be irrevocable pain. And that's what she's scared of. Mostly, unfounded, if she were to think it logically through.
She just has to call his bluff. Just has to say 'ok, Uttara talked me into it, you guys are right. Instead of carrying on this illicit affair, go on and do it properly.'
And then walk away - calling his bluff.
Uttara won't last a month. And Brahma will go berserk. The family will go berserk. But above all else, what's Brahma going to tell the entire world - that the SSP divorced his wife and married the younger sister, who oh-by-the-way was living in the house prior to the divorce?
All Devyani has to is calm down, get rid of the fear, and t hink it through. She's been through much worse, and now the kids are older, she, and they, can handle it.
-S