Two For Flinching

You all know what I'm talking about: someone fakes a punch, and gives you double for 'flinching'.  I have some theories on this fairly cruel game, but I realized it should apply to game design, too.  The problem is applying 'two for flinching' to an abstract without resorting to 'rocks fall, everyone dies,'

Well, in a roleplaying game, what's a punch?  In this case, I'm going to say major antagonists and major challenges.  I'm using these as my definition because like in fiction, the major challenges and antagonists are going to be the 'thing' that the players are going to remember outside of their own gonzo antics.  Even so, there are more stories about game masters introducing key villians or challenges and the group sidestepping it in a fairly ingenious manner.  (Or occasionally just dumb luck.)  And that is our flinch.  Sidestepping the major stuff.  One shotting the villian.

Now before anyone accusses me of advising railroading, hear me out!

We assume the event happened.  The challenge is ignored.  The antagonist defeated and broken.  Your plot didn't even limp from first contact.  What do you do?  Many sources of game mastering advice suggest bringing in a related character as an antagonist.  Even if the party didn't know about them.

What if the mechanics of the game supported this idea?  If every villian has a 'replacement' statistic that gives the game master the general level of power of the next villian in line.  It encourages the game master to make these decisions before the inevitable happens, which in turn keeps the game moving at the table.