It's actually more worthwhile to keep away from Epic Creatures and let them live, rather than kill them, because they leave, in their wake, creature parts. You are better off trailing them and collecting the bones they leave behind. Killing one only gives you 100 DNA points, which is the same as killing or allying with a Rogue.
You are better off allying or killing a Rogue. Rogues can be befriended, although it's rather difficult. If you want to kill one, one strategy I've found is to follow them until they get into a fight with other creatures (in one case, I even saw 2 rogues fighting each other). Once a Rogue is weakened from combat with other creatures, you can finish it off. It will give you 100 DNA points.
If you can ally with a Rogue, it can give great boons. They are immensely useful in both combat and social interactions, and when you advance to the tribal stage, they join you as Rogue pets!
You can kill an Epic Creature in the tribal stage but its only benefit is lots of food (if you are a carnivore or omnivore). One trick I discovered is to use Traps. The Epic will be lured to the trap and will be killed instantly when it springs, regardless of its health. You can then send the tribe for a massive food collection (100+ food).
