David Brin's novel Kiln People has this "merging back" idea, with cheap copies, using clay for a lot of the material and running on a hydrogen based metabolism so they are very short lived (hours to weeks, depending on $$) and have to merge back relatively soon in order to keep continuity of consciousness through their long lived original. Lots of fascinating practical economic, ethical, social, military, and political details are explored while a noir detective story happens in the foreground.

I recommend it :-)