Would you still find a way to convince yourself it's not true? How do you think you would react?
Nothing. I live the kind of life I want to live. I aspire to be the kind of person I want to be. Being the best (in this hypothetical case, entirely philosophical) Christian I could be would become even more important to me.
BTW, it will never be possible to prove with 100 percent certainty that God doesn't exist. One cannot prove a negative. :-)