1. If you die, you cannot reengage the group that killed you (preferably dont engage their clan/faction either) for 4 hours.
2. If you run away, and are not pursued, you cannot reenter the system you ran away from for 4 hours.
What this means is...
3. If you do NOT die, and you run away, as long as you do not reenter the system you ran away from, you may reengage the targets you ran away from.
General accepted afterburner distance is 6k. So if you boost to 6k away from the enemy, it's considered "retreating" and the victor can then either cruise to re-engage or cruise away, tasting sweet victory. There is, however, no official rule that clarifies this.