If A is true Z is true.
If B is true Z is true.
If C is true Z is true.
Minor premise:
Either A is true or B is true or C is true.

If you flip the wall switch down, the room will get dark.
If the light bulb blows, the room will get dark.
If the main power is lost, the room will get dark.
.
.
.


Now, on to the main question. Dilemma is the fork in the road. In a fait accompli the bridge that comes after the right hand fork is already down. Guest is looking for the word that covers the situation where the bridge goes down after the person gets to the fork in the road but hasn't yet decided which road to go down. I don't know a single word for that, but would use the phrase "not to choose is to choose" to describe it.