Conduct a "risk mitigation" discussion

Several folks already pointed out that you are not the decision maker and you should not pclaim to know more than your boss, all things considered.
What you can do is to express your concerns and to help your boss to mitigate the risks. The discussion may go like this: you outline the possible failure scenarios and impacts, and offer what you or your team can do to handle the situation. Remember, you can not exaggerate the risks, and you can not challenge his decisions. You have to remain positive and offer help. If he decides the risks are too great for him to swallow, that's his decision.
If your company has a formal test sign-off process, you can register your concerns and risk mitigation plan. Otherwise, the one that has to take full responsibility is your boss, not you.