I would reccomend adopting the slide down to maximize system. It is fairly widly used and makes things easier since trying to perfectly maximize within your movement range can be challenging. Its the 'clipping' section on page 7 of the FAQ/Errata found here:
http://www.games-workshop.com/MEDIA_CustomProductCatalog/m470856_Warhammer_FAQ_2008-02_Edition.pdf

It will make determining flee and persuit directions alot easier. By the system you use, the halberds would flee following path B and the spearmen would follow along path B. the rules say you execute a Turn Manouver away from the enemy and move your flee distance. A turn manouver is rotating each individual model on the spot to face the direction. The halberds would not be cut down for fleeing through enemy units because they were part of the combat they broke from, they simply pop out the other side of the combat and run from there (assuming they roll to flee farther than the spearmen persue).

If you adopt the slide down to maximize method, the spearmen would be higher up in your diagram, even with the halberds. This means you will get more models in combat on both sides, but it also means the centers of the units will be more lined up and its easier to visualize the direction people are running.

 

What about if your unit breaks from combat while facing an enemy that had both the frontal charge and rear charge?

Does the fleeing unit automatically get destroyed or do they pop out the other end of the enemy unit just like fleeing through a friendly unit?

 

Units ignore any other units that were in the fight for this purpose. Roll your dice, and if you roll higher than any unit that is pursuing, move that distance through the unit that is in the way. This is stated on Pg. 41, second column.

As to your diagram, the halberdiers would indeed flee through the white lions. They would go in direction B. Now lets assume the the white lions had a higher unit strength than the spearmen. The halberdiers would then flee through the spearmen and out the other side to the left opposite of direction B.

SirKently

 

Under the current rules, the unit is automatically destroyed, as it would be forced to flee directly away from one of the two units, and therefore into the second.
I would like to see this change in the next edition, so that the unit would flee to the side, but as it is now, the unit is destroyed.

 

That is correct. This can bring up a weird situation where say the halberds fled 7 inches through the spearmen and the spear pursued 6"s. Technically the 6"s would land the spearmen on top of the halberds, but since you didn't actually catch them by rolling the same distance or higher, you have to stop an inch away.

Just remember, you always ignore all units that are in that combat for who you can move through when you flee and you only ever catch an enemy if your die roll is the same or higher.

 

To continue on this theme, here is one that I would like some opinions on.

Lets say you have a block of 20 spearmen attacked in the front and rear. You break, but for whatever reason, neither unit decides to pursue. No the interesting part, you roll your flee and get a 2. This won't let you clear the unit that you will be fleeing through. Are you destroyed or do you flee out the other side of the unit gaining extra movement.

SirKently

 

You'd just have to be placed 1" away. They can't be destroyed since they were in combat with both units, so you just have to locate them in such a way that the rest of the rules are enforced as a "best fit" solution.

 

You'd definitely bounce through the unit.

Quote from the book pg 41:
"The only exception to this rule is that units that break and flee from a multiple combat are allowed to move through any of the enemy units they were fighting"

 

The opponent will have hit himself in the head after he saw such a poor distance