What happens to a Jew who does not apply the Halachah for himself?
All Jews are obligated to follow the laws of the Torah — of course, each one in his unique manner, and with his unique character and tools. This is the way in which Jews achieve the purpose for which they are here in the world. Somebody who does not follow the halachah is choosing to lead his life contrary to this purpose (we will not enter the discussion of how), and he is therefore subject to the harsh consequences that the Torah describes–whether in this world or, especially, in the next.
However, the Mishnah tells us that all of Israel have a share in the world to come, and even those who do not fulfill the Torah, will somehow find a way to achieving their purpose — if by means of returning to the world, or by the punishment they receive, or by other means, that are hidden with God. Yet, it goes without saying that it is far preferable for a person to achieve his purpose by means of following the halachah, than by any other means that God has to bring upon him.