Any government only ultimately governs because the people let them do so. Government, like other nebulous concepts such as money and justice, is a mass hallucination that we buy into. If people en masse refused to be governed by Westminster then there isn't much that MPs could do about it.
The key thing is that they know this. On some level, at least. And that's why the size of the mandate matters. The lower it drops, the closer people are to choosing to shake off the hallucination.
If this idea seems ridiculous now then that's because it is ridiculous. At the moment, about half to two-thirds of the public actively participate in the democratic process and I'd guess that most of those who don't are probably either apathetic or otherwise believe in the system but don't get involved. So we're a LONG way off anything dramatic happening.
But if turn-out dropped down to the 25%, 20%, 10% kind of levels, don't you think that would indicate a change of mindset? A change that politicians would have to be scared of, because it would undermine their whole existance?