We’re not obligated to remove them, but it’s fine if we do
The question of how to use author, work, and franchise tags has already been asked, and the guidelines are fairly straightforward.
If the question is asking about a) aspects of the author’s life, or b)
aspects of the author’s work that are not specific to a single work or
franchise, then we tag the question with the name of the author.
By implication, when the question is asking about aspects of an author’s work that are specific to a single work or franchise, we do not use an author tag. We use a franchise or work tag instead, as discussed elsewhere in the answer.
If the question is about a work of fiction, it always gets a tag; if
we have to create one, we do that (give it a tag wiki, etc.) If
there’s confusion over what to call it, bring it to meta.
So yes, we would use fahrenheit-451 instead of ray-bradbury.
We don’t need to ask about each individual author tag, such as brandon-sanderson, since we have a meta consensus that applies to author tags in general—at least when it come to future tagging.
The question says:
We’ve already discussed “the correct usage of individual works tags
vs. author tags vs. franchise tags”, but my takeaway from that was not
that available author tags should be removed from questions about
We should be careful when it comes to changing tags on existing questions. Part of this is for the same reasons we should be careful with any large retagging enterprise: for example, flooding the front page with old questions. If making a change would require retagging large groups of questions, it might be worth bringing to meta even if the existing policy is clear. But retagging two or three questions in accordance with the current policy is probably fine.
I would also argue that retagging old questions in accordance with current tagging guidelines is not necessary. Not much harm is done by having incorrectly tagged old questions floating around.(assuming that the incorrect tagging is of the nature of an author tag, and not, say, my-little-pony questions tagged as superman) However, editing old questions to conform with current tagging guidelines should not be viewed as negative, either. If we retag a question to have the tags that it would have if the author had asked the question today, or if they had read our various tag policies, that’s arguably a good thing. If someone found an old story-identification tagged science-fiction-genre, in contravention of our policy, then it would be fine to edit the latter tag out. The same applies for author tags.