you are right about other damns, they could have saved people to some extent in northern KP. kalabagh could save mianwali and surrounded areas and also save sindh BIG time.
but what headworks could do? they cannot store/stop water. headworks are there to feed irrigation network, which was already full due to rains. plus irrigation network could not take this much water anyway, and if they divert all the water to canals, it could have resulted in more wide spread damage, at the moment areas near rivers are affected, in that case, it could reach other agricultural lands which is somewhat safe as yet, not totally destroyed.
the most important and biggest plus point of kalabagh could have been no flood in sindh, and almost no water shortage this year for the whole of sindh and southern punjab
actually our KP and Sindhs nationalistic parties have been making this issue for no reason, just because they do not have any better cause to run in elections and rule their people, they are playing with national interests for their own vested interests, make all dams, including kalabad, neelam-jehlam, bhasha and even try to make more artificial ones downstream kalabad, make arrangements to divert the overflow water towards Thar desert, which will save Sukkar and other parts of sindh as well as convert water starved lands into irrigation lands