Get out of the school | Act 2 - Ghost of Sarajevo Sniper: GW2 Guide

Head back to the previous room and go through the next door - at some point the ceiling will fall down, but luckily it won't do you any harm. Enter the staircase and wait for the soldiers to stop walking and silently eliminate the one standing on the mezzanine.

Go down the stairs and you will reach a gym room. Silently eliminate the enemy standing by the hole in the wall and afterwards jump through it to get outside.