Over on Gaming Ballistic, Douglas Cole is discussing running away. In D&D based games, but of course I play GURPS and D&D based games, so naturally I'm thinking about both.
I posted a response, quoted in full here:
"My experience is that it's hard to run away. Part of this is because PCs often encumber themselves down with fight-winning armor and weaponry, and make movement speed secondary to victory when you finally do get in combat. Second, they're less than willing to discard gear to run away faster (a common historical and realistic tactic).
Third, and most critically, PCs generally try to run away after they're already engaged in a close-in fight and it starts to go badly. Cap that with an unwillingness to quickly choose a rear guard capable of trying to keep the enemy from pressing too close (giving you a few turns of full movement vs. their move-and-fight), and you get a messy retreat that waves between "we have to leave" and "we can't leave, some of our party members are down or can't get away." The term for that isn't a "withdrawal" but a "rout."
I have zero issue with all of this - it's a logically consequence of PC decisions about equipment and tactics, and a logical and realistic consequence of the rules.
If you do like PCs (and their NPC foes) to be able to run away, do a variation on something Archon Shiva suggested and I discussed - give Advantage to any rolls made to simply get away, or Disadvantage to attack a foe that's running away full-tilt. That way you get more survivability, and you still get the realistic effect of those closest to the foe when they turn get killed."
I'll stand by all of that. But I'd like to add some:
Mobility Matters. Running away, more than "get into that gap in the enemy's formation" or "go help a buddy," is where mobility matters. You need some before this is even a realistic option.
"These engines are the fastest in any tanks in the European Theater of Operations, forwards or backwards. You see, man, we like to feel we can get out of trouble, quicker than we got into it." - Sgt. Oddball, in Kelly's Heroes
Cut your losses doesn't mean stop taking losses. Sometimes players will figure, running away ends the combat and we can run. If we're still taking losses, it's not worth running.
But "cut your losses" means you limit the loss, not end it abruptly. You may have to pay a cost to get away - use up powerful magic items you were saving, throw away equipment to get a higher movement rate, ditch treasure to lower encumbrance and distract a foe, or even sacrifice a rear guard or two. "I'll hold them off" actually works, and it's why "rear guard" doesn't mean "guards guarding your back" as much as "guys who stay behind to hold them off." Having mobile characters who can stay behind and fight, then pull back and catch up, can buy you an escape.
If you can't accept losses, you get into the spiral of keeping fighting until, hopefully, a miracle happens and you win.
Run away when your foe isn't ready to pursue. It's worth noting that Sir Robin escapes after distracting his foe and then easing off into the distance while his foe argues with himself. It's not a straight-up contest of movement speeds. That's one way to run. If you're engaged in a toe-to-toe slugfest with foes and you're armored to the gills with heavy gear for the heavy tank battle, guess what, it's him or you. So consider distractions (nageteppo, say, or area effect magic), discouragements to pursuit (caltrops, hand grenades ticking away in their path), actual distractions (send someone to attack them elsewhere), etc.
You reap what you sow. Basically, if you maximize grind-it-out close combat, you have to resolve your fights in there. If you always run down and slaughter your foes because everyone has a 12" movement rate and so do the bad guys, know they can do it back. If you never make any effort to have a plan to extricate yourself from fights, you'll be without a plan when you need to do that.
Sometimes it's too late. One thing you have to accept is, you can't always run. Foes may prevent it, losses amongst your PCs might keep you from it, and disparity of movement speeds might stop it. Just know if you get into a fight, it's not always your choice when it ends.