Well if we now do what local trouble says but still have gorman and the mission the same:
The marines will still land and secure the colony,taking more time doing it, finding no one is there and same events happens as in the movie: finding the colonists in the atmosphere processor. They will have to go in there to find them, no drones or finding alien detection systems as somehow covenant and prometheus movies has.... they probably either send their drop ship back up to sulaco or have it landed somewhere nearby as in the movie, while they go to the processor with the apc.
The commander and gorman finds out on route that the atmosphere processor is basicly a nuclear plant and if damaged will go boom and kill them all so they change loadout from pulse rifles to flamethrowers and close hand weapons that arent armour penetrating and removing grenades.
They go in and find the colonists dead and find themself surronded, and they will still lose most fo the marines here as their tech dont help them and they dont have better weapons, but as they have a battle plan ready they fall back as they notice flamethrowers not killing the xenos but only make them fall back in fear for the flames. They get back to the apc and get out of there and decides to take the drop ship back up to sulaco. IF it was landed on the planet: same things as in the movie happens.
IF on sulaco: they safely get back and argue if they should nuke the site or as gorman and WY say and the commander would probably ask for orders: either nuking the site or let it be for more troops to arrive or wy spech ops.
Using their apc and lander to attack the alien hive: cant, its inside the atmosphere processor and cant risk blowing it, and they are ona rescue mission, not kill the colonists xD
Falling back and rearm: with what? Flamethrowers wont harm the xenos and more powerful weapons might damage the atmosphere processor and that is a one way ticket to hell.
nuking the site: would work but not until they find the colonists dead, as long as its a rescue mission they cant, and yes it would wipe out the hive and set the atmosphere processor to blow up but knowing xenos ability to survive from earth war and being resistant to radiation, its not impossible they survive.
And trash queen: the xenos have made hives underground in the expanded lore so on planets or places where xeno infestation exist, if they have their hive underground, no nuclear strike will wipe them out and will take boots on the ground to wipe them out.
