I dont think it was just the events of May but also the efforts of existing lobbying and overall events unfolding including US , EU and Middle east that led to Pakistan achieving more effective diplomatic results than India ever expected.
If the Indians were surprised in the air they were doubly surprised by the reception of the "Junta" as they term the current system by both the US and how their dollar didnt go all the way as hoped in Pakistan's traditional allies. Ironically, they were more take aback by China's open hands(based on China looking at an opportunity to break away India from the US) than anything.
They have an extensive arsenal which they can deploy which gives them enough freedom to establish a normal of sorts but they also know the much like any conflict, the script you write is NEVER the script that unfolds.
This goes both ways, they were never expecting the relative cake walk for them in 71 as it happened to be , they were expecting to prevail but with a lot more losses and efforts instead of how it unfolded.
But, and not to dither - I also have an account from someone who was part of the then equivalent to the NCA that I know but also cannot verify for any one - that the decision to "get rid of" East Pakistan was already made in the 70s.
So it comes back to the question of "stuff we hear and are pretty sure is accurate based on the individual we heard it from" but since we have no other way and that person cannot be asked to give testimony - it is what is public and no more.