The trained branch eventually flops over and a new leader will emerge from a dormant bud below the cut. You can't force orthotropy with these. I have only seen it happen once with Agathis when a plagiotropic branch was growing in a hanging basket and it was cut back several times.

I'm not sure it's apropos, but I once saw something remarkable along these lines in New Caledonia. If you travel northwards along the eastern side of the big island, you hit a rather barren rocky spot where there are a few giant columnar pines growing in isolated fashion. I heard or read somewhere that these were planted by Kanak people at a village that is now gone. (As I vaguely recall, the village's disappearance was rooted in a nasty period of French colonization.) The thing is these trees were growing sideways, straight out from the gentle slope of a cliff. Had there been a landslide? I don't know.