If you were correct, people would only leave when the net gain of running a miner became zero, which simply isn't true. Once we fall below a certain level of profitability, we'll begin to cross other folks' (and maybe my own) personal thresholds and they will pack up their rigs and go home. At this point, difficulty drops and mining becomes more profitable again.
I would include that hassle in the cost of running the mining operation.
Interesting. If mining becomes more professional, I think there will be less variation. Price also depend on news reports that increase awareness.