That territory was never meant to be, and never should've been Pakistani to begin with. 'PAKISTAN' doesn't have a B for Bengal because it was never meant to be Pakistani. It was 2000km away and its breakaway was imminent. While I do agree it could've been done in a less bloody manner, nothing could've stopped this.
Also, Pakistan annexed Chamb after the war. One could argue Bangladeshi-Indian forces won in the civil war, while the war against (West) Pakistan was more of a stalemate considering India captured no land significant value, much less retained it. Indians did not dictate to us the terms of the peace treaty, or they'd have taken all of Kashmir, Bangladesh, and much more. It was the Bangladeshis in the east dictating the terms while it was the same old story in the west where both sides have to accept each other's demands.