Decentralized Swaps cant go down. Even if their website is down their code is deployed on the blockchain and manually accessible in the event of a crash.

Tokens aren't listed on them, they exist on the blockchain. Even if they are not listed on the DEX, you can import them manually with a copy paste of their contract address.

There is no orderbook, they use liquidity pools which determine the price based on the ratio of the two assets in the pool. One gets bought too much it reduces the price of the o