Learn Turkish: Öyleyse yarın konuşuruz. - In that case we will talk tomorrow.

It is made by combining the word öyle (thus / like that / so) with the conditional suffix -(y)se (if it is). Literally meaning "if it is so", it is used as a conjunction meaning "in that case", "then", or "so".

Why is the aorist tense used here (konuşuruz) if the action is happening tomorrow (yarın)? Wouldn't the future tense (konuşacağız) be better?

In Turkish, the aorist tense is very commonly used for casual plans, promises, or intentions, much like "we'll talk" in English. Yarın konuşuruz is a natural, relaxed way to say "we'll talk tomorrow." If you used the future tense (konuşacağız), it would sound more rigid, like a formally scheduled meeting.

The current lesson focuses on aksi takdirde (otherwise). How does öyleyse relate to it?

Both are conjunctions of consequence, but they represent opposite logical paths. Öyleyse introduces the consequence if a preceding statement is true ("in that case" / "if so"). Aksi takdirde introduces the alternative consequence if the preceding statement is false or doesn't happen ("otherwise" / "if not").

Could I use o zaman instead of öyleyse in this sentence?