A scandi edge wouldn't be that hard to keep sharp for a very long time, in my opinion. If it was a true survival situation and your only knife happened to be a scandi, it wouldn't really matter if you convexed the edge to keep it sharp and functional. As long as it is sharp and does what it needs to do, who cares if you're maintaining a true scandi grind? All knives will eventually wear out over a long enough time line.
If history is any reference on this topic, it is worth pointing out that this style of knife is not even close to new. From my reading, early examples can be found that are around 1500 years old or older. I doubt that their users had anything to sharpen their knives that you could not come up with in a survival situation. If by SHTF you mean something akin to the end of civilization as we know it, time spent working to pay bills and the like becomes time to figure this stuff out. If they could do it way back in 500AD, I'd reckon it can still be done now.