How was the 747 in the China Airlines Flight 006 affected by the wing damage it sustained?
As you know the aircraft manufacturers keep tracking their aircrafts because any accident of these would damage their reputation. All automatic data transmissions are traced by the manufacturer whether the operator has a tracking contract with the manufacturer or not. Should it had an asymmetrical behavior causing any dangerous consequences the manufacturer would have made what is necessary to ground it.

In the website you refer to, it is written « After repairs were made to the plane, it returned to service on 25 April 1985. It continued in service for nearly 12 years »:

I may assume this aircraft has landed in Europe, or in USA, should it have been dangerous, it would have been grounded.

As far economical performances are concerned, that’s secondary compared to safety, it is the operator decision to evaluate to make it fly or not if it becomes less economical.