@NB
I just remembered a possible flaw in my connection to the Nexus and rebuilding, because in the LU Trailer we see Duke smash himself, but he doesn't rebuild himself. Instead, Overbuild has to rebuild him??? More likely, the smash-and-rebuild concept wasn't known to the makers of the trailer. An in-universe explanation: no one knew they could rebuild themselves yet. :P
Also, our ideas don't necessarily conflict: the Nexus Force can set up safe areas with shards of the Nexus, or Imagination generators, or whatever we want to call them / however they're made in them which can help fuel minifigures' Creative sparks, even after a smash, so they can rebuild there. Possibly they are temporary and rely on some Imagination-energy harvested from the Nexus to function - but they can aid in rebuilding. Imagination-energy is also self-reproducible, as seen with things like everlasting hiccup tablets or Fountain of Imagination which are presumably created, and spawned, with imagination.