A paradox will happen and there could be a few outcomes really, you could be stuck in a loophole of existing and not existing as you have created two different timelines, or the universe could have a way of preventing you from killing yourself on the way, resulting in no outcome, or lastly, you could have created a parallel universe and when you go back in time to alter something, that universe is created, meaning that the person will not exist in one but will in the other and therefore have to adjust to another lifestyle