I'm trying to not get too drawn into this as I don't have the time, and i'm worried i'm too set on certain things already. Going into the intial list dev with strong opinions when there's lots of other people involved can be problematic.
but here goes
Infantry:
still has the full gamut of unit types.
While they're short on bodies, they're also short on logistical support and have smaller forces generally. Each battle becomes proportionally that much bigger and important to the clan, and they're willing to risk people because of it:
Foragers: light scouts, private specialists in exploring and making safe old strongholds. Lightly armour, sneaky and often operating with small drone support (similar to tau). Typically carry a variety of personal weapons (from shotguns to sniper rifles), mines, tools ect. Drones may or may not be skimmers. A mule type trundler to carry equipment is just as likely. They are the pencil that marks the blow.
clangaurd: stronghold militia, all people take turns fulfilling this duty. Rarely caught in battle, and if so normally just to garrison areas and fortify the big guns. Typically accompany or are supported by trundlers outfitted with a heavy weapon - similar to the Marine Thunderfire cannon. May also operate with sniffer drones or animals bred to detect genestealer infestation. They are the base of the anvil.
Holmgard: lightly armoured, but carry palisade shields. Professional soldiers, dedicated to holding the tunnels in case of a breach. Due to the shields encumbrance, normally operate on the surface only with transport support. They are the flat of the anvil.
Hearthgard: elites. exoarmoured, deploying via tunnel, mole or land raider spartan equivalent. They are the hammer.
Embittered: those squats who lost the most in the collapse, and who were unable to turn to their new lives. Often drug addicts, suicidal or otherwise damaged beyond use, they seek death in absolution. Few commanders encourage their presence at the battle, but fewer yet would deny them oblivion once they arrive.
Golem: repurposed construction bots varying in size from dreadnaught to knight. Similar to the new decimator. Often outfitted with mixed heavy weapons, a clangard variant with large shield is also common. They are used as linebreakers and point holders. Some strongholds disagree whether a robot can be oath bound as they have no dilemma over keeping it or not. Sometimes known as Grudgeeepers, although other strongholds use that name for the heavy weapon platforms used y the clangard.
Gunships: heavy flyers, capably of dropping from orbit. a multitude of roles exist in society for these, but in combat they act as gunships and grid square removal services.
Superheavy versions are still in use by some strongholds, and modified cargo haulers have been used as transports in the past.
Tanks: various strongholds field various types of tank, generally considered inferior to the gunships. Emphasis is on durability instead of killing power. Gunships and tanks work in the same hammer and anvil pattern of the infantry.
Outriders: still exist, and still useful for scouts, flanking attacks and light convoy protection. Relatively rare now, and rarer still on the field of battle.
EDIT:
I guess there's two parts to this list. There's the 'drop from space and reclaim our rightful stuff' and the 'Stronghold on the defensive with only minimal survivors'.
For the talk of the drone army, if I was a a senior overseer, trying to hold everything together in the working half of a shattered stronghold and suddenly facing a ork warboss bent on looting, i wouldn't order the construction of dozens of fiddly, complicated infantry bots.
I'd order the construction of dozens of heavy crude tanks, each with a simple droid slave mind, the option to remote control and the hardpoints for conversion to other uses later.
The 'drop from the skys' force would presumably have time to build up forces before committing to the attack, so for them it might be less of an issue. Then again, rolling bunkers are rolling bunkers. I personally see them as a big mishmash of different unit types - rhinos with leman treads, chimeras with extended chassis, up armoured crawlers with a predator sponson on top...Call them Scratch Companies, Technical Drones, Bodge Tanks, War Tractors or whatever
"You seen the orders Balur? The Offcuts are riding the elevator down, dropping the last few meters right into the thick of it. Take and hold, take and hold."
"Huh? we're an anvil unit, not a hammer. Why are we doing the Sledgedrop?"
"Ever dropped an anvil on someone from 2km up?"
as mentioned before the Leviathan could be the core of the army with bikers/gyro support troops plus overlords and land trains (maybe change the berserker car to a living quarters car)...
