We don't travel at 30LY/day. We travel an 12LY/day, yes this is fast, no it's not fast enough to sustain a galactic civ.
I didn't mean that, I meant that at 12ly/d it would only take 30 years to travel from one edge of the galaxy to another, only a handful of years to travel between most of the core Citadel worlds. It really wouldn't be much more of a hassle than managing the British Empire.
I've discussed this topic to death in other threads, but basically even in the 21st century we can map out planets from a long distance, thousands of lightyears away, and I imagine with ME level computers and technology they can do a much better job of it, so any one ship with dedicated astrogational instruments could probably, within minutes or at most days, tell you the planetary breakdown of every star within a thousand lightyears of its current position, and probably also tell you a rough chemical composition of their atmospheres, letting them know without even setting foot in those systems whether to expect available fuel and discharge options.
Considering that the Mass Relays are actually an impractical way of travelling because you need to go from one to another and not just to any point you choose - it does seem like that the usage of them are more than just 'convenient'.
They're only inconvenient if they don't go where you want to go. Think of them like airplanes vs. cars. If I want to get from New York to Boston, I can drive to the airport, take a plane to Boston, and then drive to my final destination. Alternately, I could drive the entire route, and depending on traffic the travel time might even be similar, with a lot less hassle. However, if I wanted to get from New York to LA, going by plane, even if both airports are a bit out of the way, would be much faster than driving the entire length.
sure, pure FTL that can go as fast as a relay would beat using relays, but so far that sort of travel isn't even a theoretical option, but that doesn't mean that if the airports are down, driving, while not ideal, would still be an option.
But the stories following it would be about the species of the galaxy rebuilding the Relays.
Not necessarily. You can tell the story of rebuilding the relays. You can tell the story of the strife and/or unity that came from not having the relays for a period of time, and the "buccaneering" time of astronavigation without them. And
eventually, you could tell the story of the galaxy with the relays back in action and things returned largely to the state before they existed, but just as WWII greatly shaped the post-war economies of the nations involved, the lack of relays, however temporary, would greatly effect the histories of each race in the galaxy.