where

In this case, I read it as "in which."

In an extreme case, a case in which a town was...

If it's a relative adverb, as you say, shouldn't it be the restrictive instead in this case?

In an extreme case where...

It seems to me that the relative adverb and the prepositional phrase with the relative pronoun as object (in which) are completely interchangeable here. But "where" is clearly not a conjunction.

I think "in which" is more common. I think of "where" in explaining formulae, "f = ma, where f is the applied force etc."

GG's point was that your "relative adverb where

AvangiI But "where" is clearly not a conjunction.

Is it really that obvious?
This would still make sense, wouldn't it?
Where a town was crowded with a whole bunch of clones, which is an extreme case, there would be practical problems.
Anyway that is not what I really wondering about.
I first thought it might be a relative

I agree with you about the comma. You're modifying the case on both ends. If you take away the "extreme," the comma goes away. "In a case where a town was crowded etc."

If you wish to keep the "extreme," I think you'd need to say, "In an extreme case, one where a town was crowded etc." (Notice that GG repeated "a case" in her example.)

I was leaning toward sayin