DrAnjumZia,

Why would the host country (India) do that? They are literally asking for war and vengeance. What's their interest in letting a Pakistani diplomat leave for their country?

Legally, following all protocol procedures, it is exactly as you've described it. But, they have already violated several treaties, Why would they follow this one?

Also, they've already arrested the highest rank officer of the High Commission of Pakistan. High Commissioner, himself. So, why would they care about lives of junior officers?

And, there are videos on Youtube where junior diplomats are harrased by Indian government as well as civilians of India (Before Pulwama Attack, when situation was not that bad).

Diplomats don't have any security or weapons with them. So, if they are attacked by the Indian mob, they won't be able to protect themselves and their families.