One can even take this approach a bit further: atheists usually have better reasons for rejecting, say, Christianity than Christians have for rejecting other religions. That's because atheists have thought about these things and have concluded with good reason that religions are irrational. Christians, on the other hand, cannot say such a thing about other religions, at least not without compromising their own views. (I once read a Christian criticism of Islam which stated that, if there is so much as one contradiction in the Koran, then the Muslim religion is wrong. That's true... But what a thing for a believer in the Bible to claim!) If anything, then, it is the religious who should be more concerned about the possibility of being wrong.
There is, however, a better reply to the “what if you're wrong” question. The person who asks it is implying that the God they believe in will punish nonbelievers one way or another. After all, “what if you're wrong” has no force unless the consequences of being wrong are bad – really bad. Moreover, whether or not someone suffers this punishment is based on nothing more than whether or not they have the correct belief. But a good, morally just God would never have created such an unfair and immoral system. The question “what if you're wrong,” then, gives us a great opportunity to turn the tables around: it makes a good case, not for belief, but for nonbelief. Anyone who thinks it is reasonable to ask such a question cannot consistently claim to believe in a good God.