ORIGINAL: flycatch
Not being rude, when was the last time you tried to evaluate the glue joints in the tail of the plane? This is almost impossible. The appearance of the plane looked super. Hot glue joints don't survive the knock of a 100cc engine. This I believe what happened to this plane. I have several ARFs but nothing this big. The pilot did not induce this failure. Tthe manufacture did this. Many posters have brought this to light and I still hold the manufactire responsible for this tragedy.
There is always a lemon in the batch and your pal probably received the unlucky fuse. It happens.
I don't know of any ARF manufacturer that uses 'hot glue' and that myth has been debunked by Horizon and Great Planes many times. The Chinese factories normally used industrial glue guns that mix epoxy as it exits the tip. Many different formulatons can be used and most seem to use one that is a bit flexible when cured. This is actually a benefit to vibrating joints but if the formula cures too fast it lacks penetration into the wood, much like 5 minute expoxy vs. 30 minute.
Your pal has already taken the right approach by repairing and moving on. There is no disagreement to the frustration encountered and the possibility all could have been lost.
Lastly I disagree that it is almost impossible to check glue joints in the tail, especially in a 33% airframe. A couple of good twists of the tail feathers and fuselage accompanied by popping noises is the best alert I know of to potential joint failures. This works on smaller airframes too.
The best part is once it is repaired he will not have to worry about it again.