There are a few options.
if the cloud is down but the hub is up
First, if the Samsung cloud is out for an extended time but your hub is still operating, there are a few (and only a few) things that will still run, basically smart lighting automations that use only devices with local handlers.
The following thread discusses this in detail.
You can see what you have running locally on your own account:
http://thingsthataresmart.wiki/index.php?title=FAQ
If the hub goes down
Next, if your hub goes out it’s no different than any zigbee or zwave controller going out. The only option you have in this circumstance is if you have previously associated some Z wave devices with each other for direct association. But that’s not typical in a smartthings set up because the direct association to do not report to the hub and so things can get out of sync. But it is possible.
In either case, your devices still have value
It’s important at this point, however, to note since smart things uses standard zigbee home automation and Z wave devices, even if your hub was destroyed and the Samsung cloud was not available, you could still keep all of your other devices and move them to a new controller. Exactly which controller and which devices might vary, but you certainly should be able to preserve a large amount of your device investment. sensors, switches, smart bulbs, etc. should all be able to work with other controllers.
secondary controllers?
As far as having something that can run locally when your smartthings hub was not operating, you can’t do that for any zigbee devices which are connected directly to the smartthings hub because a Zigbee device can only have one controller at a time.
If you have your smart bulbs on a Phillips Hue bridge then you would be able to continue to use those bulbs through that bridge connection. But zigbee bulbs like Osborne Lightify or cree just wouldn’t work.
Z wave, however, does allow for the possibility of secondary controllers. Smart things doesn’t support all of the command sets available for those, but you can set up a simple connection. Some Community members do have a Staples connect or a vera (both of which can run locally) acting as a secondary Z wave controller to their smart things hub. But it won’t run any of your smart things routines or smart apps or rule machine. It will only run schedules or scenes that you have set up on that secondary controller. So it will fit some use cases, but not all.