It seems to me that the spirit of the 4 hour re-engagement rule for retreating would count for same system as retreat occurred in only.
If player B runs and leaves system Q that should be the end of encounter 1.
If player A then travels to system X (that B had fled to) any encounter there should be considered encounter 2 and separate from encounter 1.
Deaths would of course mean player B avoids player A and system Q for 4 hours.
