I had a conversation with him about this a while ago.
On one hand, I don't think RPers have the right to say "you can't dodge" under any circumstance. If you want to force a certain outcome, it's your responsibility to create a foolproof plan. This issue, and others, is worth discussing at some point.
On the other hand, you have to allow him enough information to work with. The difference between "he is dead" and "he looks like he is dead" should NOT be kept secret from the other writers, but for that very same reason, you may have to reveal some plot-specific information earlier than you'd like, much like you did when I asked about Reversal Mountain. Not to the characters, just to the RPers.
In the example you gave, I think he overstepped his power as a player, and you chose the wrong time to call him out on it. Details that, again, can be worked out later if need be.
I need to log out for a while; thanks for taking the time to explain that to me.