Yes, TopoFusion works well offline. As long as you download all the necessary aerial photos beforehand, it will work fine.
You can either pan around to get the maps you need to make them download, or use the 'reload / load' maps tool to draw a box around your area(s) of interest.
Once a map tile is downloaded, it will always be accessible. This is different than google earth and world wind, which have limited tile caches.