Hang on a second, while I go blue sky.
First. I can't really see FOtLK being moved into Theater in the Wild (Nemo theater). The stage layout and seating would require a total re-work of the show, or a re-build of the building, plus that means that both shows would likely be closed at the same time. I just don't see them doing that.
So, what if they re-configured and expanded the Flights of Wonder theater and then move FOtLK into this new venue? Closing that show to make room for Lion King would have a small impact on overall park capacity and they could keep the Lion King show open during all but the final phase of construction. Plus, that theater is in a prime location, between Asia and Africa.
Although, if they were crazy, and decided they were really going to use Theater in the Wild for LK, they could move Nemo to DHS in either the Mermaid show building, or the Beauty and the Beast theater. This seems like a good fit for that park.
At any rate, I don't see either of these shows being retired in the near future. They're both still really popular.