Still some people here asking for detailed, mechanistic explanation of how a non-HP scaling RPG would work and deal with Dragons vs. PCs and such. So...
In games like RQ, the better the armor was at damage reduction(sans magical enchantments), the heavier and more cumbersome that armor tended to be. Plate armor was better at preventing damage from a sword thrust than studded leather but it also weighed at least ten times as much.
In RQ certain skills having to do with bodily movement/maneuvering(including stealth, dodge etc.) as well as magic skills, were penalized with encumbrance. Most humans in full plate were not going to be dodging someone's granma wielding a purse and they counted on the damage reduction of their armor as well as their shield parrying skill to avoid damage.
This effectively limited 'thief' type characters to leather armors because of the encumbrance alone, without need of artificial restrictions by class. Same went for mages/shamans/priests. Hard enough to cast that really powerful spell in just robes...no one wanted to subtract 50% from this so they could wear chainmail.
Unless you magically increased your SIZE or CONSTITUTION attributes or wore some magical HP increasing trinket, your HP did not go up. An encounter with a dragon in RQ was a lot like a scene from Dragonslayer. Nasty stuff. A party had to have their magical preparations in order...defensive spells vs. fire, buffing spells for the warriors/archers, offensive spells that could penetrate the dragon's hide, etc.
If a warrior was going to act as a 'tank' and go toe-to-toe with a dragon, he would need some deity-forged quality armor. Otherwise the attackers needed exceptional dodge ability and such. Trying to parry a dragon's swipe with anything but a deity-forged quality shield(and even that is a doubtful proposition) would leave a stain as testament to that PC's passing.
Dragons themselves did not have massive hit points(average dragon had 53...about 3x - 4x the average human warrior) but their 24 point armor(all damage reduced by 24 points against them), flying ability and massive damage dealing capacity was immense.
Success in RQ was measured in degrees in that if you had say, 100 sword skill any roll(using that skill to attack) of...I think 20 or lower(1/5th of skill level?) resulted in a special success and any roll of 5% or less(1/20th of skill) was a critical success. Rolling a '00'(for a person with 100 skill) resulted in a fumble.
When dodging/parrying a 'special success' was required against a 'special success' attack roll by the attacker and a 'critical' to avoid a 'critical' attack roll.
So the bottom line for a static HP system is that the simplistic 'Hp increases with levels' is replaced by pertinent skill increases, better armor, etc. No one is shrugging off dragon's claws because they have 10,000 HP from years of adventuring. They are eitehr doging/staying the fuck away from those claws and/or they are well armored/protected.