What happens if Coinbase shuts down?

Could you please elaborate on what potential consequences might arise if the cryptocurrency exchange Coinbase were to cease operations? How would it impact investors and traders? Would their funds be safe? Could they still access their cryptocurrencies? Would they be able to withdraw their money? Would they lose everything? Could there be legal implications for Coinbase or its users? Could other exchanges be affected? Could this potentially lead to market instability? What steps should investors take to protect themselves in such a scenario?