I don't have much experience with the Variable Speed pumps, but I would imagine they should behave the same in a power outage as they would if they were unplugged, or the breaker were tripped. You could try that to find out what happens if you have a power outage.
I don't see any reason you can't leave the pump and SWG running 24/7. You just want to be careful because by changing the run time, you will be adding to the on time of the SWG. SWGs typically run at a percentage. So at 10% they are on 6 minutes out of every hour. At 100% they are on the whole hour. So if you normally run during daylight hours, lets say 12 hours (I run most of my pools from 8am to 8pm), and you run it for 24hrs while you are away, you are running the SWG twice as much and generating twice as much chlorine. Since your solar cover will be on all day every day, you won't see as much loss of FC from sunlight, so you will see FC levels rise. So basically, you will be overchlorinating your pool by running 24/7 at your normal setting. I would probably turn it down to half what it normally runs at if it is going to run 24/7. If your CYA levels are good you will most likely come back to a pool with high FC, which is better than a green one. If that happens, your FC will start to come down on its own once you return to the normal schedule. You can help it along by turning off the SWG for a while. Just keep an eye on the FC levels so that you don't have algae start to grow.