I found myself in the same situation - Locus could not do an address search offline. My instance was more complicated because the destination address was in another state. But I found very easy way around. I manually downloaded available vector maps of US states and than being online did destination address search and created navigation route (you can use either departure or destination state.) After this you need to open map of the second state and make sure that you can see destination/departure location.
From now on, every time you open departure/destination map (offline) you will be able to see your route ( do not forget to pull the map of new state when you will cross the borders of departure one .)
From now on, every time you open departure/destination map (offline) you will be able to see your route ( do not forget to pull the map of new state when you will cross the borders of departure one .)