The inevitability of combat is far from guaranteed. Note Gygax's rants on "superior play" in the AD&D Players' Handbook, explaining resource management, goal-setting, focusing on treasure and avoiding unnecessary fights. Also note the experience system that reinforces this model by giving more treasure for gold recovered than monsters fought (in many ways the original story rewards for games, though the story was always about looting the underworld). But what makes me really see this are minor rules in the AD&D Dungeon Master's Guide that establish frequency of monsters and how they interact.
Gygax's random dungeon tables make only about one in five rooms in a dungeon include a monster.
The reaction table means that most monsters will not attack, at least not immediately. There is room for parley and diplomacy.
Morale rules may lead groups of monsters to route rather than fight to the bitter end.
This suggests a different mode of play than I encountered as a wee lad, one build around exploring a mostly empty catacomb, looking for treasure of any sort and avoiding danger as much as possible while doing so.
This difference in assumptions is central and promotes a different feel than later editions as the game developed in different directions than original play in the first campaigns. And as I tweak the rules, understanding the difference will be important as I consideeranways to support and reinforce my preferred styles of play.