Flash reversing time in Zaddy's Justice League has some implications.

The reason Flash managed to reverse time was because of Einstein's Theory of Relativity. Time slows the closer you get to the speed of light, and time stops completely at the speed of light (this is called time dilation). So logically, one could assume that surpassing the speed of light would cause time to move backwards.

However, here's the issue. Time dilation is only noticeable to the entity travelling at the speed of light. For an observer, time would pass normally. So only Flash went backwards in time, and not the rest of the Justice League. That means the original timeline Justice League is dead and the ones that are alive at the end of the movie are alternate reality Justice League.