Update: The plan is to return my guitar to Japan for restoration of the finish. I added the following proviso:
"I want to make sure that a complete inspection confirms that the heat/humidity did not cause any problems with respect to glue joints, bracing, warping, etc., or in any other finish areas. These are difficult to observe or hidden problems that could occur depending on the intensity of the heat and the length of time the instrument was exposed to the heat. As well, I would assume that the master luthiers and the designer will do a comprehensive assessment to ensure the guitar is in pristine condition before it is sent back, but I just want to be sure of this. If any other problems are uncovered, I would like to be notified. I would also like to know if the entire top will be stripped and refinished (which will require removing the bridge)?"
I also suggested it would be a good idea to confirm the handling conditions during shipment...airline, broker, customs, etc., so this problem is not repeated. At the very least, the shipping container should indicate that as well as being fragile, the instrument should not be subjected to extremes of heat, cold or humidity. Even better: If one uses a bigger box lined on the inside with 1/2" thick styrofoam insulation and then foam peanuts, the guitar case is then surrounded by insulation and foam peanuts inside the shipping carton. This can insulate the instrument and thus mitigate some of the potential for heat/cold damage.
The estimate for restoration in Japan is two months; add 6 weeks to apply for and receive the Canadian CITES export permit and another month for transit...I may see it in February, 2018, so it's unlikely to have heat issues on the way back..just cold and dry.
Time to practice more with my GC-10...