Fall apart? Well, I don't think it was ever intended to be whatever 'together' might mean. Katas - such as the Jo kata - are just collections of ideas/principles. If you don't suss out what they are and then take the principles on board by practising them in other contexts then all you have is the form. How could you possibly expect to be able to use a Jo in combat by just practising kata? Of course, that is all they give us, and so, with that in mind, it is up to us to go figure out what to do with these new principles we discover.
I dont think that Rob was thinking of "using a Jo in combat" when talking about fall apart but rather the way that aikiken/aikijo is designed to instill a specific way to move, and itīs that specific way of moving that falls apart. Does a boxer stop moving like boxer under pressure?