That's the problem with incomplete analysis. Just see what percentage are these flights of the total flights of PIA. Also compare the size of India vs Pakistan and hence the amount of detour that the respective flights have to take if India is closed for Pakistani flights and vice versa. Also remember that its only flights from Delhi airport that need to fly over Pakistan. International flights from Bangalore, Hyderabad, Mumbai, Chennai etc all bypass Pakistan anyway. On the other hand, irrespective of where the flight takes off from in Pakistan, if its going to Nepal, HongKong, BD or south east asia, it needs to go over India.
You may have to close your flights to bangkok, Dhaka, KL, Beijing etc if India closes its airspace
Bangkok and Kuala Lumpur are marginal routes for PIA and in the current low season, they are losing money. Beijing flight is routed across PURPA intersection and then through to China - it doesn't even go anywhere near Indian FIRs.
Dhaka is the only significant PIA route that would be impacted and in any case, dropping it would be manageable.
Also, it is not only flights from Delhi that would be impacted but those from Hyderabad, Bangalore and Mumbai too.
Here is the great circle distance which represents the shortest flying distance from the Southern India airports to London. They all transit Karachi FIR:
1 The fuel cost will be high which will hit your bottom line
2 To recover higher fuel cost if you increase fares then you will be uncompetitive. People will prefer to fly to dubai and then take flight to these destinations
3 There will be huge increase in time of flight by going around India.
See above, traffic to the Far-East is relatively small from Pakistan compared to the Mid-East and EU destinations which are the greatest revenue generators for PIA.