Which is in my eyes not a problem the DM has to address. If the players don't let the PCs run away, even when facing overwhelming odds, it is their decision.
Not every encounter does need to have multiple escape routes. Imo the DM should make sure that the location where the encounter happens fits into to world and let the PCs figure out how to escape. Some locations will naturally have more and better escape routes than other. Thats just another challenge the PCs have to deal with.
Why should the DM check if the PCs have bought items to help them escape? If the PCs run away and wath items to use for it is completely in the hands of the players and imo the DM should not make any changes depending on the PCs having items to help them escape or not.
And if those items are available depends on the setting and location.
Also, what would you do in the case the PCs don't have those items?
I never said for the DM to check to see if the PCs brought the items. I said the DM should check to make sure escape is feasible. Whether the players do the smart thing is the player's problem. Whether they plan ahead is their problem. Whether the observe the environment and see their opportunity is their problem.
What this thread is about is how the DMs can make running away more feasible. Because many people do not think it is feasible, so they don't do it. Points that don't address solving that situation, is like talking about how alcoholism isn't a problem in a discussion about how to get over alcoholism.
@Morrus;'s got a great point, that removing the safety net and killing some PCs may change the player's mindset about the proactive steps they should be taking. It addresses a change the DM can make to bring running away back into consideration by players.
To clarify one more thing for [MENTION=2518]Derren[/MENTION], I feel like you're threadcrapping here because you're not addressing ways to enable running away, you're washing your hands of the problem which does not change the existing situation that PCs don't run away. Any of the ideas listed here aren't going to be literally and fully executed by anybody. I don't expect the GM to absolutely supply every encounter with a deliberate escape route.
But it's something he should consider, especially on encounters that are blatantly more powerful than the PCs. If the PCs walk into the room and there's a mega-CR monster, just what exactly did the GM expect would happen? Direct combat is inherently a TPK waiting to happen. So clearly, the PCs needed opportunity to get clues that this monster was in the room before they entered or an escape route. If death is a forefone conclusion, the encounter SHOULD be designed with other opportunities embedded in it, otherwise, it really is just a deliberate campaign killer.*
*on various other threads about level appropriate challenges, just about every DM who says hog-wash to that and has much stronger encounters appear also incorporate clues as to its presence. No good DM introduces a TPK-monster in the next room that was unavoidable if the party paid attention or exercised any caution. The point of such encounters then tends to be to test your avoidance skills or running away skills.