The current D&D Next play test rules for lethality and dying are way too soft for games that I would like to run. I want there to be a greater threat of death, for a number of reasons, but not least because I don’t want combat to be the first resort of PCs. Mike Mearls has already said that HP is likely to come down, but I don’t think that is enough. The dying rules also have to be addressed.
The thing that frustrates me about this discourse is that it is not an either/or proposition. It is easy to build several possible play styles into the core. First, you can always start at higher level. Some people object to this because higher level is also higher complexity, so you are really affecting more than one aspect of character design (though I’ll also note that a first level 4E character feels about as complicated to me as a 5th level traditional D&D character). Including options for different play styles does not take anything away from anyone else.
The various editions have already given us a plethora of death rules. All that is needed for 5E in this regard is for them to pick several possibilities that address different play styles and present them, along with pros and cons, in whatever becomes the referee guide. For lethality, three natural options jump out at me. For a lethal game, dead at 0 HP (perhaps with a constitution saving throw to be incapacitated rather than killed). Other options would be dead at negative 10 (or negative constitution) HP, and the current playtest version that is reminiscent of 4E (with all those fiddly death saving throws) could also be retained as an option.
Here is a proposal for supporting different levels of lethality. Vary starting hit dice. This has the advantage of not increasing complexity for other character aspects. Also, First Edition play falls out as a natural corollary (the 1 hit die variation). One die of self healing is also very close to common binding wounds and liquid courage old school house rules. Bump the starting hit dice up to, say, 4 or 5 and you will have a game that feels much closer to fourth edition; starting hit points will be greater, and PCs will have more hit dice available for spontaneous healing.
The other major aspect of lethality that is potentially problematic in Fifth Edition is the recovery provided by a long rest. In the play test rules, a long rest restores all HP and hit dice. This should be another part of the game with a menu of options. I would suggest recovery of one hit die for an old school feel (which would then need to be spent for any healing to occur), recovery of all hit dice for a less deadly but still random feel, and recovery of all hit dice and HP for a super-hero feel.