Pakistan as an idea happened in 1931, so it is actually plausible for it to disappear. The driving force here would be the Princely States wanting to remain independent. Baluchistan, Kashmir, Hyderabad, Mysore and Travancore would essentially split off from India, and sign a treaty of peace with them, while the rest of the Princely States fall. India, being more violent and possibly authoritarian in the wake of the war of independence, alienates Bengal and Assam, who become new states on their own. Tamil Republic splits off later, as it is isolated from the rest of the country, and sees little representation in Delhi.
And the existence of a Sikh state is impossible, considering that without partition, the Sikhs won't constitute a majority anywhere.