If you think about the challenge of using a single person to act as a metaphor for a country keeping them in one place is going to lose some of the power that moving them around would have.
So the movement into exile in Pakistan comes when Sinai’s family breaks apart after it is revealed that he is in fact not their son but was swapped by the nurse Mary. She disappears into her own exile having destroyed her relationships with her employers and the relationship between everyone becomes strained.
The upshot is that amongst the mourning for Sinai’s failed director uncle, who commits suicide, there is a breakdown between relationships between Sinai’s mother and father with the former being dragged to Pakistan with her mother and the later staying behind surrounded by nothing but failure and the rubble of the bulldozed estate.
The crossing of the border is not only physical but also something more powerful and prevents Sinai from communicating with other Midnight Children and enjoying his gift of telepathy.
He still suspects his mother of infidelity and by encouraging a naval officer to confront his adulterous wife Sinai believes he has taught her a lesson. The only lesson he does seem, to pick up is that children need to be beware of dabbling in adult lives and chain reactions can lead to death, murder and family breakdown.