Did the fight between Orochi and Saitama happened in the webcomic like it just happened in the manga? I readed the webcomic a while ago, and I dont remember the battle between Orochi and Saitama. Did it happen? How did things turn out to be in the webcomic in comparison with the manga?
Orochi does not exist in the webcomic.  Instead Gyoro-Gyoro is the official leader of the Monster Association, rather than its "Military Advisor" and shadow leader.

The wiki's trivia section for Orochi indicates he may have originally been intended by ONE (who came up with the character for the manga) to provide a better challenge to Tatsumaki and the combined S-class, perhaps to create an opening for Gyoro-Gyoro to disable Tatsumaki.