Golbez, Crystal Collector's last ability checks at the moment it would trigger to see if you control four or more artifacts. If you don't, the ability won't trigger at all. If it does trigger, the ability will check again as it tries to resolve. If you don't control four or more artifacts at that time, the ability won't resolve and none of its effects will happen.

If the target creature card is an illegal target as Golbez, Crystal Collector's last ability tries to resolve, it won't resolve and none of its effects will happen. Opponents won't lose life even if you control eight or more artifacts.