Not necessarily - the DM still puts the challenges, the players/PCs still have to overcome them; but those challenges involve exploration and-or stealth and-or diplomacy rather than combat.
Yes, but why do I want to learn a whole new system when I've already got one that'll do?
Part of this stems from my long-held contention that D&D shouldn't have social mechanics, and that introducing them in 3e was a dreadful mistake. Social interaction in D&D should IMO be settled through roleplay, with mechanics either extremely minimal or absent altogether - which means that D&D already works just fine for a non-combat game.
You'd still use the D&D chassis to roll up the characters, to equip them, and so forth; and for the parts of the game where mechanics were still required e.g. exploration, stealth, etc.