A friend is planning on moving. If he does so, can he do so without re-installing the zigbee and z-wave devices already installed? (I know he will probably have to repair these connections, but,...)
If you shut everything down, and disconnect and then reconnect, it should work, but obviously you might have signal routing errors that will be harder to track. As you have read here, a strong mesh of powered devices added by closer to further is the best way to do it. Unless i had under 600 sqft, i would recommend to restart from scratch. Will probably spend less time debugging in the future, then the initial rebuild.
I think it could be done, but hasn't there ever been a time where you said "If I could have done it differently, I would have". This is the perfect opportunity to do so. I think there'd be less problems if your friend started over just because the system would go whaco for a while before everything started routing properly again. Lots of unknown errors and such. IMHO
If your friend is going to be doing a lot of re-designing of the system then yes, I think that re-setting would be easiest. But, if he's going to move a lot of the devices to the same room in the new home (i.e. kitchen motion sensor moving from old kitchen to new kitchen) then there is no reason that he can't leave those devices paired to the hub and therefore not have to rebuild those automations. The prospect of having to rebuild everything from scratch is a daunting task and avoiding some of that would be welcome to me. Remember that zigbee devices will go into "panic mode" after about 20-25 minutes of being powered on without the hub present. After which each device will hunt for the best route back to the hub. This in addition to time will heal your zigbee mesh. You can also force a z-wave repair to fix the z-wave mesh. Now, there are several caveats to this. This would mean that you would have to move the entire mesh to make sure that you have the enough signal to reach the hub for each device.
No matter what your friend decides to do, make sure he/she pulls the batteries from any battery powered devices. Searching for the hub is the most power-hungry function of those devices and it'll gobble up juice quickly. In fact, if the devices are older (60-75% of their battery life), it might be a good idea to just put new batteries in when re-mounting those devices just to have full battery life to start off with.
In any case, I would love it if you'd post what your friend decided to do an how that worked out. Especially if your friend decides to "cut and paste" the system in a new house. In theory, if they started close to the hub and worked out with implementing them back on, It'd be interesting to hear about. At least i'd be very interested in hearing about it. The question has been asked before.