AI can design chains of its own. But will they last long enough? If there's lack of interest/demand among people, AI-generated chains won't survive. Even if they do, how would they pose a direct threat against Bitcoin? It doesn't make any sense.

What AI can do is manipulate the market in an attempt to crash Bitcoin's price all the way to $0. It would practically "kill it", since most people are only in it to make money. But the core Blockchain network will remain alive and running as usual. Decentralization-wise, only governments and "Wall Street" will pose a direct threat against it. People still hold most of the circulating supply (as well as run most of the nodes and miners), so I wouldn't worry about this in the time-being. Just my two sats.