He could've passed the torch to someone else or even sell the thing. I'm sure many people would've jumped at the chance.
Except...no, not necessarily. Being an old-style webmaster and managing servers and whatnot is a huge amount of work and requires a lot of time and energy. If you wanna run a website like E-hentai you have to be dedicated to it. Selling a website to a new webmaster would be pretty reasonable ten years ago, when independently-owned websites were commonplace, but nowadays with 90% of the content on the internet being created and hosted on like 4 or 5 sites, nobody wants to bother anymore. Believe me, I've personally witnessed the death of a 10+ year old forum site and it went down something like this. Site upkeep got too expensive and too time-consuming, so they figured it was best to close the doors.
He was the admin, yes, but he had a staff working with him developing new features for the site and optimizing it. I don't think it would be unfeasible to leave one of them in charge.