What's the deal with this? Reddit already stores a local copy of all kinds of external images (external-preview.redd.it). So in an optimal scenario, when imgur decides they no longer need the driving force of porn images, because they are now so pure, so big, so divine and so clean, nothing will disappear, since reddit has copies of every linked image on their servers.
Well that depends if that's actually permanently stored or not, it's very possible it just caches a short time
The former policy of allowing NSFW images from mobile apps but not from desktop browsers was dumb and contradictory. It created a ton of confusion. I hope they update their pubic facing documents and help to accurately reflect what they are really actually doing.