Note that Engineers will not be ‘used up’ by this repair process - they keep existing outside of the trench. This is very much intended for trenches: an Engineer would not be repairing/rebuilding an entire building, just re-digging a trench so his work would not be too exhausting.
Buildings that are used as rubble via Rubble.Destroyed are not allowed to be occupied or have passengers of any kind. Capturable rubble is not supported.