Raghav has promised to take santosh out of haveli so that she escapes. I think he has an inkling about the chautala guy and hence taken her to mela to make her escape. OR in the mela he will come to know about chautala guy and make her escape with him. I think i am thinking very far fetched when i say he will be planning to marry her off to chautala but that may also happen one day. May be Jogi can die and a widow remarriage issue can be raised through santosh and chautala.
I think the reason he has not told sia is that if she tells the FF gang there is chance of the plan getting leaked out to avtar through chanda and then to rangeeli. He knows how mean rangeeli is and hence will not tell anyone till he executes the plan. Once he executes he plans to tell Sia about it. Sia has one problem she cannot hide her expressions very easily like when santosh was hiding in havel ishe showed her nervousness on face which made ammaji doubt that santosh is in haveli. Same with other FF gang. If ammaji will threaten them they will blurt out the whole plan. So it is best Raghav keeps it a secret till its exceuted and santosh has run very far away from ammaji's goons.
But this plan of Rgahav will become redundant because Santosh truly becomes pregnant and ammaji gets kidnapped. Hence he may have to abondon santosh running away plan for time being.