you are right. it took them so long to clear the part of slide to ease the flow. I would say such a big slide to remove is not possible but geological survey already mentioned B4 the land slide that this area need attention.
Anyways now the lake is 300 feet deep and 20 km in length upstream with about 100 cubic meters of water per second of out flow. Now they have to stabilize the lake banks, the spillway and the near by rock by whatsoever manner, bolting, shot-creteing. They need to increase the outflow in a control manner so that lake levels should go down. I am sure something might have been done. This lake is now matter of life and death for country. God forbid in case of a failure and opening of the dam, I read an article another 200Km of KKH will be drowned, many villages and the major damage to tarbella or almost it will be washed away..