Is it obligatory to delete a blog that gained popularity due to publishing an explanation that was thought to be used for something unlawful, and then was deleted, with doubt about visitors continuing to follow it thereafter, and the blog owner's desire to profit from it?

There is no need to delete the blog simply because of what happened previously, and there is no harm in keeping it. However, one must be careful not to publish anything that is impermissible or aids in what is impermissible. What is used for both the permissible (halal) and the impermissible (haram) may be published. But if its use in the impermissible predominantly outweighs its use in the permissible, then publishing it becomes forbidden, due to the Almighty's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression."