First, I want to make a huge apology regarding this post and my inactivity. This post had been submitted through our inbox on 2/19/2017.
So to add to this in detail:
earthsenshi has submitted a theory stating that Rean will still be with Thors in Sen III, and that he will be a Soldat instructor. See the cut below for more details!
Proven Theory Notes: While Rean is not specifically a Soldat instructor and not at Thors itself, he is most definitely an instructor at the new branch of Thors- Thors II- as revealed by Falcom on 3/9/2017. Close enough to land the ‘proven theory’ tag on this one. Good work, earthsenshi!