I have been running my C4 hub for a little more than 2 years now, and it has been running flawlessly. The only thing with C4 is the decline of free memory over time, which I get around using a scheduled reboot twice a week.
However I have been wondering, what's the lifespan of a hub?
At the moment if my hub dies, there is no easy way to get it back up and running. I would have to order a new hub and wait for it to be delivered, then I would assume loading a backup copy my C4 settings/rules into the new hub and manually re add all my devices (all my devices are zigbee). Just the thought of all these steps gives me chill 
What's your recommendation for a backup plan/failsafe in the event of a hub fail?
Get a new hub and then you have a backup hub(old hub) if the new one fails.
Actually, you've got it easier than someone with all Z-Wave. With Zigbee, if you restore the backup, you'll only have to re-pair devices, but they'll be recognized as the same device and will slide right back into place in apps and whatnot (one exception: if you're using Groups with Zigbee Group Broadcasting, go in and hit "Done" to re-configure the group ID on the bulb/switch). Z-Wave would create all new nodes/devices you'd have to swap out. 
With a C-5 or newer, you have the option to subscribe to Hub Protection Service, which will take care of Z-Wave. (Zigbee is the same either way, but it's also a bit easier for the above reason--aside from needing to touch all the devices.) With a C-4 or older, manual migration is the best you can do. Keeping a spare hub around wouldn't be a bad idea if the "waiting" part seems like the most difficult. Otherwise, my hope is just that this is a rare event for most people. I have a spare hub I could use (currently use it for testing and development), but I have yet to need it and hope I don't, at least not before I decide to migrate to something newer, if/when that comes, on my own (a process I recently finished with the C-7).
