Ok - AJ's full stage is un-useable (bad reg or something), happens in the restriction so he goes to his bungee reg. Then meets up with Litehedded and in the process of aligning directions the post rolls off. Momentary alarm and the crises funnel begins.
Might be planning for multiple failures, but it's the best I could think of without (hopefully) being too unrealistic.
Hunter
(posted at the same time as James' post above)
I think your scenario while not impossible is just something you cannot really "plan" for, but experience and not "going ahead of your experience and abilities" can help to keep a calm head and resolve such issues
Regarding your scenario
#1 - If I personally was approaching a small/silty restriction, I would not be doing anything to my stage during the restriction.
If I was close enough on gas on the stage I was using, i would go to the new stage first (drop the empty) and verify that the new stage is working before entering the stage
#2 you should feel a rolloff and be instantly back there to turn the post back on.
#3 your scenario doesnt seem much different than a diver with say just doubles, in a small silty area getting a rolloff --- what part does the stage add here ?
#4 If I can access my bungee reg in a restriction, then I can probably access my longhose too. So unless a real CF is happening, thats probably what I would do (because I can now donate). If I cannot go to my bungee then I am in some dire-sounding trouble!
If the restriction is small/silty then I think you (one) will already be hyper-vigilant when approaching it.