Glad I stopped in on this thread. I may have some work for that Boot Repair Company, a pair of Meindl where the mid-sole has fallen apart. They don't make that boot any more, and another similar pair would require much driving and trying on, then probably a £200+ price.
I have had a pair of Clarks dress shoes fully resoled, and the result was unwearable, so I believe there is an element of risk as to whether any resoled footwear actually works like the original. With the Meindls the risk of throwing £60 down the drain for the chance of saving £200 might be worth it.
Sorry, not sure about the Jungle Boots. They look like it might be possible to cut off a worn sole and bond on a new one, but I think I would be concerned about using them in a jungle afterwards. Would be a bummer of a place to learn if glue isn't quite good enough!
I have used consumer grade glues to get more life from day hiking boot soles, but that was just little bits, and the glue never held for long, best was a few months of dry and fairly smooth use.