At the start of my current 4e campaign, I made this very simple decision about the game world. The ramifications of this action have been fairly profound, and they have changed the play style at my table for the better.
Every Encounter Means Business
This was the most obvious set of changes to be made. I need to really think about the encounters I design now, since a failed Death Save in an early battle can spell total disaster later in the adventure. Encounters where the party can neither run away nor surrender mean there is a potential for TPK, which is even worse than normal.
The Players Take Threats Seriously
Discretion is the better part of valor. When confronted by the enemy, the PCs in my game now make a point of carefully sizing up their opponents. They are aware that a heroic last stand is just that – a last stand. When in real danger, a fighting retreat to better terrain has become a common tactic.
“Face” NPCs are More Important Now
NPC allies have become a huge portion of my campaign. Companion Characters frequently join the heroes in combat, allies lend financial support, and the crowd that generally surrounds the party grows as the heroes become friendly with more and more people. I encourage this, because every friendly NPC has the strong potential to become a PC in the future. I try to provide an eclectic cast of NPCs for the players to draw from in the event that a hero dies. Losing a character is less traumatic, both to the player and to the story, if there is another character he or she is already emotionally invested in. If the party barbarian dies, then it is easy for the wererat orphan she has been raising to step up to PC status.
I have found that my, “dead means dead,” rule has really enhanced my game in ways I did not at first expect. Have you tried something similar? How did it work out in your campaign?