Can a part of the group remain stealthy when combat starts? D&D 5e

A group of 4 PCs roll stealth. They sneak around and 3 of them get noticed by the enemy (because of line of sight or just bad stealth rolls). Combat starts, everyone rolls initiative.

If the remaining PC has a stealth roll higher than the enemy’s passive perception, does he remain in stealth? Can he then go around to get an attack with advantage on that enemy (while remaining out of sight)?