Dying?
By this time, after seven battles with his imitation, Davis had drastically improved in his usage of Essence Gathering Cultivation as well as keeping heavenly fire and heavenly lightning together. It must also be known that he hadn't reached the level of combination and could only stick them together, thanks to both heavenly flames and heavenly lightning being yang in nature.
Although they were destructive and could explode upon contact, his heavenly physique made it so that he could easily keep them unagitated until they hit the target.
Now, it was possible for him to combine them, drastically increasing their prowess.
However, what made it possible for his imitation to learn combination shortly after him?
Myria's imitation was too prideful. Since that imitation also had the advantage, it didn't bother to comprehend insights from their battle and tried to wholeheartedly kill the original. Hence, its laws weren't up to par with Myria's.