There is apparently a discussion on retreating from combat in D&D where a number of people are reported saying that trying to retreat is pointless because the monsters will always pursue and the result will be a "total party kill". This simply is not my experience in many years of playing D&D. Retreating works 9 times out of 10 assuming the party does a fighting withdraw (instead of turning and running in rout) and decides to retreat before they have so many wounded and dead that they really don't have a chance no matter what they do.
I can only think of one TPK that resulted from retreating from combat (as opposed to turning and running away). In this case, our party thought we were on the 2nd level of a dungeon when we really on the 5th level. We retreated done a passage that we thought was safe, but discovered that it was not the passage we were expecting (because of a teleport trap we had not detected) and we "retreated" into some even more nasty monsters.
Of course, we have always played under TSR-style rules where NPCs have morale checks. When your hirelings and henchmen start leaving in droves, it gives the PCs a big hint that it may be time to break off combat before it is too late. WOTC systems seem to lack morale rules which means players don't get this nice warning that it may be time to retreat before its too late to do so. I've also been told that WOTC editions of D&D lack rules that allow the GM to determine how long monsters (without specify orders to pursue) are likely to continue the chase. TSR editions had rules for this, generally allong the lines of these rules from my upcoming Microlite81 game:
Avoiding Monsters [Dungeons]: Unintelligent monsters normally automatically attack. Intelligent monsters may follow their orders, make a reaction check, automatically attack, etc. depending on circumstances. Unless surprised a party may try to flee to avoid a battle. Monsters will generally pursue if there is less than 120 feet between the two groups. Monsters will only pursue around a corner or through a door on roll of 1 or 2 on a d6 (1 if a secret door is used). Fire will deter many monsters. Food will distract many monsters: unintelligent monsters 90% of the time, semi-intelligent monsters 50% of the time, intelligent monsters 10% of the time. Treasure may also distract monsters: unintelligent monsters 10% of the time, semi-intelligent monsters 50% of the time, and intelligent monsters 90% of the time. All chances may be adjusted by the GM depending on circumstances. These same rules determine how monsters will pursue if the characters disengage and retreat (or rout) from a battle.
Avoiding Monsters [Wilderness]: Unintelligent monsters normally automatically attack. Intelligent monsters may follow orders, make a reaction check, automatically attack, etc. depending on circumstances. Unless surprised a party may try to flee to avoid a battle. Monsters will generally pursue so long as the party can be detected, there is a 50% chance monsters faster than the party will catch it (30% chance for monsters about as fast as the party) in each hex traveled through. Woods or swamp reduce the chance of being caught by 25%. Monsters will pursue into another hex on the map 50% of the time. The chase continues until combat occurs or the monsters break off. The party must rest for one-half day for each hex traveled during a pursuit. All chances may be adjusted by the GM depending on circumstances. These same rules determine how monsters will pursue if the characters disengage and retreat (or rout) from a battle.
In my opinion, dropping rules for morale checks (for NPCs and monsters), reaction rolls for encounters, and rules for avoiding monsters/retreating from combat is a major reason why so many people seem to expect all encounters with "monsters" to not only automatically result in combat but combat to the death. The game is not better for this, at least in my humble opinion.