[exdsq]

There are some economic and game theoretic elements in play here. Say you wanted to reverse a trade and could afford a 51% attack, the cost of the chain would drop massively so you’d not benefit by having a load of Bitcoin. The whole community could just fork from that point and pretend it never happened. And people with skin in the game would fund mining to keep the security up to avoid this happening.

Overall though the number of miners will reduce to a small group because the cost is prohibitive, however it should still be secure.