What about an SMB who already has the mitigations in place (everything is set up correctly) for a single-DC environment?
What about automation? What if AD cannot be reached, so a bunch of other automatic checks take place, and if determined, automatically restores the DC? This would be rather simple to set up.
Not sure how this is even germane to the discussion. We are talking about best practices and recommendations for AD implementation.
No, no one was discussing that. That's not the topic of this thread, and you introduced both the discussion about AD practices and then later about best practices. At no point was I discussing best practices and I saw no one else discussing it either.
@Obsolesce later stated a BP, long after you had introduced it. But from what I've seen you two alone are discussing BPs. Everyone else is discussing "possible options".
How is "most commonly correct approach" different from a best practice?
Completely different. One is "51% or more" and one is "essentially 100%". In no way are they similar.
For example... the "most common correct approach" to commuting is to drive by car. More than 51% of commuters should use cars (given current housing and work locations.) If it was a best practice, it would mean that no one should walk, bike, or take a train. So clearly, very different.
A "Best Practice" means you shouldn't even question it, you always do it. So BPs are insanely rare. We assume that exceptions can exist, so think 99.999% use case, not really 100%, but exceptions are so rare that you never consider that it might exist for you because it's unreasonable. Majority case you never, ever do blindly, because as much as 49% of all cases don't match.
That distinction might be clear in your mind, but it wasn't clear to me, nor do I think to more than a few others. I also think that your definition of a Best Practice is different from the common usage. To most that I talk to a Best Practice is something you do the majority of the time, the best option from your selection of options that is sufficiently better so as to make it your "rule of thumb". A common Best Practice recommendation for SMB is having your DNS service on your DC.