They would ban exchanges from operating within the US, which would render Bitcoin useless for 99.99% of US users. I don't think they'll do this either, but they don't have to do anything fancy to make Bitcoin worthless for the average citizen.
It's in the US's best interest to embrace it.
Edit: the best downvotes are from people that missed out on the technological innovation of a lifetime.
Then it's going to stay alive. Look at Uniswap, Sushiswap, 1inch.