To take the internet down as a whole would be a mammoth task indeed. With the networked nature of the internet, there’s hundreds if not thousands of elements which would need to cease functioning for it all to stop. Many of which are highly secure, protected facilities or underwater cables, etc. I’d say it’s highly unlikely for it to all fall down unless something really bad is happening in the world. Popular links which tie countries or continents together can break or be destroyed (such as the cable in the sea near india(?) which got damaged recently and disrupted a lot of internet traffic), but that just slows things down or makes the odd site unreachable. You could end up with something like that which disrupts your connection to the ‘net and makes everything unreachable for you, but again, unless the world was really up shit creek, that would be fixed relatively quickly. I don’t think it’s a rational fear. If things have become so bad that the whole internet is down, you’ve got bigger things to worry about than not having access to your music and photos.