It is possible to hypothetically get out of the Covenant level.
1st method
When you get to the first tower, do not enter the structure. Instead, kill the enemies outside the structure to make the process easier. Destroy the Shade also. Position your Ghost directly between the wall and the base of the Shade. Once ready, boost up and aim for the roof of the tower. This may take a few tries however.
After achieving getting on the roof, continue using the ghost to climb up the ramp until you reach an invisible wall, preventing the Ghost from moving any further. Get off the Ghost and use it as a base to jump onto the top of the wall. Proceed up the ramp and jump onto the snowy edge. If you fall, do not fret as you will be floating mid air. Once you got on the mountain/hill, you are now freely and officially out of the map.
What to do?
There are limited things you could do in this Vacation. One of them is skipping the whole level till the end. Once on the mountain/hill, proceed towards the end of the tower structure. At the side of the structure, have one player going down the hill. If the player manage to stay alive, the other player would be able to go down the same way.
Be warn that this method is advised to be practised only in Co-Op play as failing to do so may result in repeating the whole process again (If done in Co-Op, any mistakes can be fixed as the player who dies will spawn at the same location as the other player. Be warn that doing this Vacation will result in being stuck in the level as no enemies will respawn in the level.
2nd method
When battling the two Scarabs, go onto one of them and make it "stunned" by taking out the legs. Once you done that, get on the legs and stand at the "knee" of the Scarab. Wait until the Scarab recovers from the "stun" and it will knock the player randomly anywhere in the air. If the player is lucky and alive, they will be on a mountain or another structure although this is rare. Another method is to use your hornet and quickly get to the scarab on the left that "roars" and lifts up. To not get automatically killed jump off of your hornet as soon as it gets to its highest point. Then rush to the back and blow it up. You will be blow usualy towards the mountains and theres a better chance of surviving if you have the invincibility power-up so you do not automatically lose your shields. Most players doing this act would die instantaneously, flying in the air and passing every invisible wall, resulting to what some players call, stretchy Spartan. This could also be considered as a vacation although you will not be able to venture beyond it.