The old version of maps/navigation had a declared place in maps where you could save a map to the device for offline viewing. Since they did their push to combine the two into a single app in June/July or so... the only way you can do this now is to zoom to the map area you want, and search for "okay maps" (this is a really hacky way to do it) and it will save an offline version of the map to the device.
Personally, I think Google has really dropped the ball on this one, and shouldn't have combined the two applications until AFTER the resulting application was better (all the same old features and possibly more new ones) than the previous old ones.
You might want to look at the Google maps API (which I have not yet done) and see if there is a way to request a cache be stored of an area. (or if this is a future goal).
As for drop in replacement... I'm not aware of one.