I appreciate your feedback.  

I agree that it would be a precarious balancing act to keep things tense without scaring off too many potential players.  I did have the idea of introducing 'lesser trials' that would not result in character death.  The idea was that players would not always know whether or not a trial will result in character death, and hopefully this would both lengthen the amount of time that players get to remain in the RP and encourage them to take care in how their character attempts to help or trick other characters.  I would imagine that if 'A' betrays 'B' in an effort to save himself only to find out that the trial didn't cause 'B' to die that it could create problems for him in the future.  Thought it might add a layer of strategy and encourage caution in how characters and players interact. 

If a player drops out in the middle of the RP, the only course of action I've thought of so far would be to write them out and (hopefully) replace them with another willing player.  Though this would bring its own set of problems: it's unlikely that the new character would fare as well as the established ones that have been there from the beginning.  Players probably wouldn't feel nearly as attached to new blood as they would characters that they've worked with (or against) from the start, and it would be kind of shitty if they were introduced just to be quickly killed off.  It's an issue I'll have to think about further.

It's definitely not an idea that everyone would enjoy or be interested in, but I'm very curious to see if it can bear fruit.