in the attempt of a miner/pool coup, the coin would just drop to 0 as trust in the (trustless) system would be seriously hampered.
Then the price should be zero right now, because the tot 4 Chinese miners
can do a coup (e.g. by imposition of the Chinese government).
Why is it not zero? Because bitcoiners have rationalized that problem away, claiming that it is the "economic majority" that matters and that everybody would commit financial seppuku if the miners (rather than the Core devs) tried to change the protocol in any way, therefore the miners will never do it.
Neither of those claims is grounded in evidence or common sense. What is more likely is that a subtle change in protocol imposed by the miners (such as a postponement of the next halving, without changing the 21 M cap) would be rationalized as "harmless" or even "good for bitcoin"; and the "economic majority" would just submit to it. (BIP100 is going that way: it says that the Core devs should "decide" the blocksize issue by handing over the decision to the miners. No wonder that the miners like it...)
May I remind you how BTC's price reacted when Ghash.io had 50% of the network? It crashed.
Did it? When was that? How big was the crash?
I recall that there was much affliction among the people in the know, but BitFury promptly removed themselves from GHash.io and the problem was quickly forgotten.