[Nottom]

If he plays exactly the same all the time and is a winning player then he will be a long term winner.

More likely though, even if he is a winning player, he is costing himself money by playing this way.

When he is winning, then it is more likely than average that he is playing at a weak table and therefore has a higher EV than normal and should play longer. Thus in this case, quitting early is often costing him money.

When he is losing, especially when down multiple buyins, its more likely than normal that he is either tilting or at a tough table and is therefore not earning as much as normal. So this situation also costs your friend money.

So basically your friend is probably hurting his winrate significantly.