Picture this (inspired by the new Halo 5: Guardians cover art, tl;dr at the bottom):
Above the smoldering surface of a war-torn Sangheilios stands a mammoth Forerunner construct. Below its vast span labors a Promethean army, the size of which has been unprecedented since the days of the Human-Forerunner War. Banshees piloted by determined Sangheili from the Covenant Remnant fly overhead, bearing destruction and betraying the land of their fathers with plasma and fire. As the Forerunner construct moves steadily over the expanses of city, laying waste as it advances, a fleet of Wraiths, Shadows, Ghosts and Revenants at its feet ensures that no heretics are overlooked. Across the city, Jul 'Mdama stands upon the highest balcony of the ruins of Vadam Keep, bolstered by the height of Kolaar Mountain, where he cherishes his victory and the day of judgement.
Four heavily clad warriors move inexplicably silently and gracefully through the immense remains of Vadam Keep, eliminating Sangheili radicals undetected. Spartans Kelly-087, Linda-058, Frederic-104 and John-117 advance through the entire ground level in mere minutes with incomparable efficiency. It is a long journey to the pinnacle of the massive compound, one that a team of Spartan-II’s certainly could have made quicker than a team of Spartan-IV’s if it had not been for the mid-level entry point of Locke’s team via a cloaked ONI shuttle. Locke’s team had no intention of beating Blue Team to the top, however – they would cut them off.
Lying in wait for their Spartan predecessors did little to supply them the upper hand. Arriving on the second level by use of the grandiose stone stairway, Blue Team almost completely avoided the initial barrage of deadly rounds unleashed by the hit squad. Blue Team began maneuvering from cover to cover toward their attackers like a well-oiled machine while Locke’s team slowly drifted backwards, attempting to lengthen the time until their inevitable clash. The assailants became the assailed. Only the loud crack of an SRS99-S5 AM round grazing Fred-104’s forearm halted their momentum. Now on even footing, both squads allowed a brief second to pass after the sound of the Sniper Rifle fire dissipated. The brief second became two seconds… then five seconds. The moment the echoes of the shot withdrew, another one took its place. The humming of dozens of Phantom and Spirit engines approaching: even the incredibly vast estate and the relentless churning of a thousand thousand solders could not drown out the sound of the sniper fire. All eight soldiers slowly retreated from their cover, picking up their pace as the roar of the engines grew louder. The thunder crescendoed to the point where the structure started to reverberate when the first plasma bolts began raining down around them through the myriad of gaping holes in the structure, adding to their number. As the barrage laid waste to the already decimated edifice, the middle levels began to collapse – the levels directly above the Spartans. All eight Spartans broke into a full run toward a newly created opening to the exterior still steaming from plasma, no longer paying heed to one another, as massive hunks of stone and metal hailed around them.
An unspoken agreement, most likely based on the equivalence of their species rather than their loyalties, instantly took effect as the Spartans hurdled over large boulders once a part of the ceiling, walls, and floors and burst through an opening in the wall. Reaching the exterior, a massive decorative pillar, taller than even the height of the building, received a direct blow at its base from a large bolt of plasma, shooting stone fragments in every direction as it failed to support its own weight. The pillar hesitated and began to lean toward the building as a Spirit dropship landed on the upper level – 'Mdama’s escape plan. The massive column had already chosen its angle of descent, however, and it was headed straight for the dropship. The Spirit had no time to maneuver, and the stone pillar struck its starboard loading bay, sending it crashing to the ground in flames. The pillar fell against the roof with a mighty quake, though the structure did not falter. Now resting laterally along the side of the building, the pillar provided a diagonal point of entry straight to the roof – straight to Jul 'Mdama.
It was only the agility and cunning of the team of Spartans that prevented the bombardment of plasma from eliminating them. The gunners would adjust their aim, and the Spartans would adjust their path. They mounted the fallen pillar and began traversing upwards toward their target when two of the attacking dropships took direct hits from behind, resulting in two blowouts of superheated violet. A squadron of Liches had joined the fight, and were definitely not on the side of the Covenant Remnant and Prometheans. All at once, Banshees approached from both the as-of-yet untouched remainder of the city and from the fleet traveling with the Forerunner construct, and they were headed straight for each other. The two fronts of former-Covenant and Covenant Remnant aerial craft converged in a cloud of explosions. Two of the allied Liches touched down on the roof while taking Banshee fire. The Spartans reached the top of the structure right as Thel 'Vadam, the Arbiter, dismounted, touching down onto the rooftop of his desecrated home. From the other Lich disembarked Rtas 'Vadum and several Sangheili under his command. Both Liches had only just dropped of their passengers when they we engulfed in fuel rod explosions. Across the expanse of the roof stood Jul 'Mdama accompanied by a host of Promethean Knights, Sangheili Zealots, and several pairs of Mgalekgolo.
By this time, the gargantuan Forerunner construct had made its way to a mere hundred yards from where they stood, striking down countless Banshees and Liches fighting alongside the Arbiter with neon beams of hard light. With Jul 'Mdama possessing one half of the Janus Key, the Forerunner construct would not dare destroy the Spartans, the Arbiter, and the structure in one fell swoop. The construct created a large shockwave that rippled through the air as it lowered itself closer to the rooftop, transforming its shape. Streams of orange light emitted from its core as a single figure proceeded from it, levitating closer and closer to the gathering of warriors. His armor assembled itself around his body as he approached, its design matching that of the Forerunner construct. The Didact.
What do you guys think? Obviously, I don’t think any of this will happen in the game, but how epic is the thought of it?
tl;dr – Blue Team, Locke’s team, the Arbiter, Rtas 'Vadum (the Shipmaster), Jul 'Mdama, a company of Prometheans and Mgalekgolo, and the Didact all converge for en epic showdown upon the rooftop of the ruins of Vadam Keep on the Sangheili home planet of Sangheilios.