I mentioned a modified mook rule in my post on speedy GURPS combats. I didn't describe it, so I'll fix that here and write it up.
For those paying close attention, I mentioned this a while back on the SJG forums, where you can see other takes on the the "And Stay Down!" rule from GURPS Dungeon Fantasy 2, p. 27.
Briefly summarized, "And Stay Down!" has fodder drop from any hit that does damage, and worthy and boss critters stay up longer and/or get some HT rolls to stay conscious. That's a little too undifferentiated to me, and I feel like it de-values the high damage attacks of front-line fighter types by making a lucky tap from a weak fighter and a high-damage skull shot from a heavy weapon into effectively same thing. Knowing a monster is probably a mook, it means you're best bet is to use the lightest tap you can (a Defensive Attack with a thrust of a double-dagger weapon, say) to take something down.
I prefer people really open up on fodder and show their stuff, yet I want them unimportant NPCs to drop without dragging out a fight uselessly.
Here is my variation:
Unimportant NPCs automatically fail HT rolls to stay conscious, avoid stunning or knockdown, or to stay alive. This means that a wound that takes them to 0 HP or below will put them right down and out of the fight; a wound that cripples a limb or inflicts a major wound will stun them and knock them down.
(Clarification: Unimportant NPCs still get a HT roll to recover from stun, they just don't get one to avoid it in the first place.)
Special Cases: Some monsters come with special rules for staying awake - berserkers, for example, ignore knockdown and stunning, and do get to make HT rolls, no matter how "fodder"-like they are. Creatures with Hard to Subdue have it for a reason, and get rolls to stay awake. Hard to Kill means I make a death check to see if a creature is dead, even if it drops unconscious automatically.
Doesn't this mean a 2-point advantage like Hard to Subdue turns fodder into a potentially tough fight? Yes, it does. Hand out advantages that make weak monsters stand up longer with care - putting them on an NPC says you intend this guy to stand up and fight longer. It makes guys with those advantages and makes berserkers a really different fight.
Important NPCs use the full rules - they roll anything a PC would roll. These include named NPCs, boss monsters, singular monsters (if I put one chimera in a room, it's automatically a special chimera), etc. They don't have any automatic drop levels other than dying at -5xHP (unless they've got advantages that say otherwise.)
Also, NPCs might be special because of the situation. The goblin messenger who's running the alarm to the other goblins might get rolls because he's situationally important. The dinoman champion is special, even if his dinomen buddies are not. The one orc who happens to be wielding the magic sword from the treasure pile is special, no matter how weak he is.
I'll also rule on the fly that what was supposed to be a mook is an important NPC. If a fodder monster scores a critical hit, or somehow pulls off some amazing rolls (say, a great set of defensive rolls, or knocks a PC down), or otherwise shows his awesomeness, I declare then and there (silently, not out loud) that he's no longer a mook and gets to make his rolls.* This way any given mook can turn out to be important just because of what he does.
These rules apply to NPC hirelings, too, but not full-out Allies (you paid for them, they roll) or special NPCs.
This approach speeds up combat, especially with large numbers of fodder types. They don't last long if they fail to defend, but they're still touch enough that you need to hit them hard enough to take them to 0 HP or less. This lets you use them in larger numbers (fun!) without ending up with a lot of bookkeeping and rolling and status tracking (not fun!)
Coupled with the Untrained Fighters rules from GURPS Martial Arts p. 113, this makes a clear line between skill and lack of skill, toughness and lack of toughness, importance and lack of importance. It also rewards high-damage strikes and makes you use the skills you've got to dispose of the weak opposition instead of encouraging you to take out just enough to win.
TL:DR version: Don't roll HT to stay conscious for mooks; they just fail. If you give them a name or Fit or Hard to Subdue or something, you're saying they aren't mooks. Roll for them.
* This is the "Sgt. a Wood" rule. Sgt. a Wood is the name of a sergeant counter from Cry Havoc. We used it on a battlemap to represent a no-name NPC in a big fight in my old GURPS 3e game. Oddly, he fended off a much more powerful PC, hurt another one badly, and then started to escape when the fight went bad. A PC pursued him ("I'll show that guy!") and in the process got cut up, knocked out, lost a fine knife, and ended up losing out a lot in the subsequent game from trying to finish him. From then on, whenever I'd use that counter for an NPC they'd open up on him with maximum firepower and get him down ASAP.
Amusingly, one of my players made a military PC who was a sergeant, and named him Andy Wood. "Call me A. Wood."