They absolutely will leave them idle if the market is so saturated that no one will pay enough for tokens to cover power and other operational costs. Demand is elastic but will not stretch forever. The build out assumes new applications with ROI will be found, and I'm sure they will be, but those will just drive more investment. A massive over build is inevitable.
No one is leaving an H100 cluster not running because the power costs too much - this is why remnants markets like Vast.ai exist.