I can see this work for a story, but for a campaign that actually lives day to day, time travel is rather problematic. An enemy who can only time travel to the future is going to become irrelevant really quickly :) though a new one could emerge from the distant past. Go to Comment
This could easily be the start to a great campaign. Hints at an greater story than has been revealed thus far, and the genesis of any number of powerful villains who quickly spread out from the scene of the impact to pursue their own plans of conquest or vengeance.