Love your ideas Rel; in fact, I've shamelessly stolen most of them for my campaign!
Also, I've been toying with the idea of a wound/injury system based on the disease track. Call me weird, but I kind of like the disease track.

Anyway, what I was thinking was something along the lines of this:
Critical Wound
A particularly devastating attack seems to have ruptured something. Attack: Special; if a creature suffers critical damage, roll a saving throw after the encounter. Add a cumulative -2 penalty to the saving throw for each critical attack suffered during the encounter. Failure results in a Critical Wound.
Endurance improve DC 12+level of the attacker, maintain DC 9+level, worsen DC 8+level or lower.
Special: If the target suffers additional critical attacks while suffering from Critical Wounds, the target must make a saving throw after each encounter as with the initial attack, or immediately worsen.
Track:
Cured
Initial: The target loses a healing surge that cannot be regained until cured.
Secondary: The target loses all current action points and cannot gain action points from milestones.
Final Stage: The target is slowed. The target gains
Lethal Injury. Lethal Injury The pain is unbearable, and you are bleeding internally. Attack: Special; if a creature falls below 0 hitpoints due to critical damage or suffers the final stage of Critical Wounds, make a saving throw after the encounter. Add a cumulative -2 penalty to the saving throw for each failed death saving throw. Failure results in a Lethal Injury.
Endurance improve DC 14+level of the attacker, maintain DC 11+level, worsen DC 10+level or lower.
Special: Whenever the target fails a death saving throw while suffering from Lethal Injury, the target must make a saving throw after each encounter as with the initial attack, or immediately worsen.
Track:
Cured
Initial: Before the target attempts to use a daily power, it must spend a healing surge. If the target has no surges remaining, it takes damage equal to it's healing surge value.
Secondary: As with the initial effect, but using a daily power requires 2 healing surges, and using an encounter requires 1 healing surge.
Final Stage: The target dies.
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So, any thoughts?
TPK? Too clumsy, perhaps?
EDIT: Realised that I'd forgotten to add any mechanism to reverse this condition other than making skill-checks (such as a ritual). Feel free to come up with something! :P