The world would be a different place because so much happened as a knock on of that but at the same time it's hard to imagine what the world would be like. Probably very similar but also different in substantial ways.
Like obvious things like no war in Iraq or Afghanistan (at least not those wars), and less obvious things like how the attacks have reshaped liberal democracies like the US and Europe (for the worse imo), and how they empowered right wing politics in many countries (also bad imo).