Just maybe, it's a risk, but it won't happen. Miners make a living by mining Bitcoin, If they collude with each other to attack the Bitcoin network, it also means that they accept to crush their rice bowl. Not a single fool comes to see what he has created, crumbling.
Risk means for me - a risk. It can be happen. Nobody calculating with it, I see also... ... ... What an amount of wealth here just tends into a black hole. I am wonder.