Boeing isn't relocating to Wichita,  it is just going to have the fuselage
sub assembly done in Wichita.  A transfer of about 500 jobs.  Finally
assembly,  wings, engines, wiring, interiors, doors, landing gears,
hydraulics, etc will still be done in the Seattle area.   FWIW,  the 737
fuselage assembly has been built in Wichita for almost ten years.  The
portions of the Renton plant where some of the 757 fuselage is built date
back to WW II.  Moving the fuselage assembly to Wichita makes good business
sense (wages are same),  it will open up some  space in Renton for more
final assembly.

Long term final assembly of all the planes might move to Everett. (or at
least there has been speculation in the news papers).  Even if they do that
Renton would still have a large Boeing presence.  The engineering design
building are near the plant but outside of the plant (Renton) proper.
There isn't room in Everett for all the design teams to move up there --
and it doesn't make sense,  the flight test facility and systems test areas
are near Boeing field.  If they do move up to Everett, I'd guess that they
would also work on consolidating more of the design into the former Renton
campus (in new buildings) (my speculation again).

Twenty years ago,  it was the Renton Plant against the Everett Plant.
Small planes vs. Big Planes.  Boeing has tried for years to change that
environment into one of a common purpose and company.   They have been
changing attitudes and as they do that it is possible to see cases where
Small planes and Big Planes had duplicate facilities.   They're working on
sharing facilities now and eliminating that waste.  Just like any other
changing and evolving business they will redistribute work and activities
trying to get the best use of the plants.