Information is definitely out-dated, and you shouldn't really take it to heart.
Evacuation had an objective that was the same as Campaign, but had Sam, the first and only NPC in DEMO. Sam was supposed to be protected by the survivors and one could even be a sort of fatherly/motherly figure for Sam, protecting and allowing Sam to follow the player.
This was the most played game mode, as people wanted to have cheap, troll-like laughs at the reactions of their comrades as they made Sam jump into the water. Players also wanted to play this simply for a shift of change in the cycle of three maps on Survival.
It was removed mostly due to trolls with Sam, time limits, and overall just being harder on anyone who chose to be Sam's guardian.
- Protect Sam.
- While in DEMO, Evacuation used to have a time limit, but this was later removed.
- It is unknown if this Gamemode will ever be added back.