Lu Qing's so-called last resort was the virtual spirit manual.
By the time he broke through to the Dharma stage, his attainments in the void Spirit manual would not be bad. If he really reached that stage, he would have to kill people. Lu Qing could also use Weiyun's physical body and spirit to create a Dharma-level avatar.
However, the ethereal spirit chart could only grant a doppelganger an ability equivalent to his own. The other clones could only use the power of their original attributes.
At that time, he would give up the previous clone and give Wei Yun's corpse and soul to make a clone. With the power of the Taishang Scripture, his combat power would probably be even stronger than when Wei Yun was alive.
However, Lu Qing did not wish to do that. He wasn't Chen Man. Firstly, he wasn't that evil. Secondly, if he made a clone, it would be completely different from a living person. A clone wouldn't have any growth potential.