Is "then" a coordinating conjunction?

Consider this sentence:

Every grammarian believes that sentence is correct.

But now consider this sentence:

In this sentence, we have left out the "and" that connected the two clauses. Are we allowed to do that?

Some grammarians say "yes." They argue that the adverb "then" (for most practical purposes) should be considered an honorary fanboy. They believe that there is nothing "wrong" with this sentence:

Other grammarians disagree. They don't like that sentence. They say that it is a mistake (a comma splice). The say that if you want the sentence to be grammatically correct, you either have to leave in the "and", or you have to use a semicolon to splice the clauses. In other words, they see it like this:

It's a bit of a complicated debate. For now, just be aware that if you want to play it safe, don't use "then" to connect two clauses; always use "and then".

Instructions for the Quiz

For the sake of this quiz, assume that you are a very strict grammarian, and you don't believe that the adverb "then" should ever be used to connect clauses.

Fix each sentence on the quiz, fix it by doing one of the following things: