If you haven't got your portal I don't think you can do anything with your copper and granite mines anyway. The only thing to keep in mind is if you like those Dwarven roads, you'll never be able to build any more of them as soon as the copper and granite runs out. Some people build up a little extra at the end for that reason.
It has nothing to do, I recall that quest, it confused me.
The game assumes you have broken streets and teaches you how to fix them.
#1: Disconnect a building (so it shows a forbidden sign above), like, cut the road that comes out from your Main Hall.
#2: Add the road you just removed it (but first you need to see the building(s) disconnected.
#3: Quest will be complete.
It's an odd one, but yeah, it's there hehe. I guess some players might have disconnected buildings and not notice it.