They don't even have to rebel. God is the giver of life, and life is His to take back if He so chooses. This is how we were always taught. God did not need a reason. Since He is the personification of mercy, the fact that we are alive at all is due to his merciful nature. Most (if not all) Christians will admit that we are not deserving of life, that it is a gift granted us by God.
And that God is also the personification of justice. Which means He would be justified in taking back that which was given undeservedly. Imagine living for an eternity with that particular sword of Damocles hanging over your head.